I always see self-checkout as outsourcing the cashier's job to a slow untrained amateur (the client) whilst doing away with paying for that work.
You need to be a sucker to choose to do work for the profiting of others without getting anything at all in return for it (at best, what you get is less slow checkout that the manned tills which they purposefully made worse than before in order to push you into self-checkout, which is not in fact better than what you had before, so not really a "benefit").
Even in the most purely amoral "greed is good" judgement, it doesn't make sense to do the work without at least getting a discount.
It's absolutelly possible to just go through the thing as if the cashier was an automaton, in which case it's still faster than self-checkout.
Personally I like the challenge of getting a laugh out of a tired cashier (especially if it's a pretty woman), but nobody forces you to engage that person beyond a purelly utilitarian acting your side of the process you're part of whilst the cashier acts theirs as if you were both machines.
It's a weird problem to have not to be able to stand facing another human who doesn't really care about you enough (or has the time) to engage in small tall, whilst being fine with standing facing a machine with particularly unappealing software which cares not at all for you and won't engage in small talk ever, but I suppose if using the machine solves your discomfort with machine-like human-action then it's a valid reason.
I'm gonna be honest, I fucking hate standard checkout. They are slow, there's always a line and usually only 1 in 4 checkouts is open, at least that's like it where I live. I know in the US there are like a thousand people working at checkouts and people use the cashiers as therapists or whatever, but that's not it where I live. Usually self checkouts occupy 1/4 of the space, or even less, than a normal checkout, are faster and are always open.
Even better, where I live they've started implementing mobile scanners that you pick up when you enter the store, scan stuff as you go, and then checkout in literally 10 seconds. Just walk up to the self checkout machine, scan the special barcode and pay. There may be random checks where you need to go through a standard checkout and confirm the self scan. I believe they use an algorithm where, if your scans are usually correct, you get less and less random checks, until it's basically none (or the opposite).
In the main supermarket where I live there are, iirc, 44-46 checkouts in total. 14 are standard checkouts, usually 6 or so open, then there are like 12 or so self checkouts and like 18 self scan checkouts. The standard checkouts occupy more than twice the space as all the others while doing a fraction of the throughput.
BTW, I believe the discount is the time I don't have to wait in line. If you also want to sneak out something though, you do you, couldn't care less, it's not like you are stealing from the poor.
Well, as I've wrote somewhere else, I have some minor expertise in evaluating business processes because of my job and I lived in London (UK) during the time when the largest supermarkt chains really started pushing self-checkout (the retail market is quite concentrated there)
I've also seen some attempts at that done were I am now, Portugal, in some supermarkets as well as how cashier operation can be done extremelly efficiently at the Lidl supermarket I used to shop in when living in Berlin.
From my observation when they install self-checkouts the supermarkets will not only reduce the numbers of manned tills but seem to purposefully reduce the number of people manning the available tills so as to push people to use self-checkout, and this happenned both in that transition in the UK and here in Portugal for the few supermarkets trying that, all noticeable because checkout via manned tills becomes slower when self-checkout is introduced compared to before that, something which logically does not make much sense without the "pushing people to use self-checkout" motivation (logically, with more tills in total waiting times at any till, manned or not, would become shorter, not longer).
Also there's an interesting psychological effect applicable here which is that time passing when waiting feels a lot longer than time passing when busy (such as when doing the actual self-checkout), which in this situation means that even if the total time from queuing to leaving is longer because it takes you longer to scan all articles and pay, it can feel shorter if the waiting time is shorter.
(A interesting "sciency" experiement here is to actually measure it with a chronometer)
So yeah, if you look at it from an "in the moment" and not at all systemic point of view, it does seem that when there are self-checkouts they're faster than manned tills, both because you're not really counting operating-time like you count waiting time and because the supermarkets very purposefully underman their tills to push people into self-checkout, probably because their long-term objective is to cut down on manpower hence boost profits (which is also why they won't give you a discount for using self-checkout as that would go against the whole profit-enhancing motivation).
Funny enough I just wrote a post about my experience with Lidl in Berlin when I lived there.
The previous poster has no clue at all about how that whole thing can be an extremelly efficient process with proper cashiers and cooperating customers that would actually become way slower if you used self-checkout instead.
(I actually have some minor expertise in evaluating Business Processes from my job and like to evaluate the efficiency of all kinds of work processes I'm looking at, and efficiency as a cashier has a lot more depth than button pressing and article scanning - for example, merelly memorizing the position of the barcodes in articles can easilly make a cashier go several times faster. More broadly, with all the time I have free whilst waiting to pay at the supermarket, I often entertain myself spotting the unneeded time waste and it's amazing just how big of a fraction of time is spent with stuff like waiting for customers to put their change in their wallets).
Then again this being Germany and Lidl the cashiers are actually normal store employees that will do whatever needs doing, on proper employment contracts and paid significatly more than cashiers in most countries get, as Lidl is known for investing in its employees - and expecting them to be much more flexible in the tasks they'll do - rather than deal with them as easilly replaceable "human resources".