We used to get plenty done with much less screen area, so there's isn't really a driving need, per-se. There's nothing wrong with that workflow, even today.
That said, more pixels does enable some useful possibilities. IMO, the major difference comes down to using your peripheral vision (which wasn't possible before) and less background tasking. Both converge on less cognitive load since you don't need a mental map of what's in the background (everything is "foreground" now). Instead, you can scan your immediate environment (screen real-estate, physical devices, etc) to find what you want. And I think it's ultimately a matter of taste: some people will find that overwhelming instead of helpful or useful.
No, I'm with you. I think it's needless most of the time. People are arguing uses, but Star Trek really takes it to a needless level. I remember an episode of, I think, TNG where someone has to be trained and is given a big box of PADDs to read. Jake has a different PADD for everything he writes.
I have a two monitor system on my desktop and I do use all of that desktop space, but there's a limit to how many screens I could see myself ever needing.
And really, you would think Starfleet would come up with something more efficient.