I never understood the appeal of the business in the first place. Why would you care who your great great great grandpa was? I don't even care who my Grandpa was.
It's commonly used by Adoptees to find their biological family. This can be important for a few reasons, including finally getting accurate family health history.
i had a coworker from my last job find his birth mother through one of these dna websites. the happiness he had on his face when he came back after finally meeting his biological family made me think about 1) how fortunate I am and 2) how many people have used these services to connect to long lost family members.
No question. It took me 6 years and thousands of hours to find mine (distant matches only, and birth father was dead, and birth mother was also adopted, which added an extra 2 years to the search). If it wasn't for DNA I would never have located her though.
About 10 years ago they provided medical data from the samples. I used 23 And Me too confirm that a health problem I'd recently been diagnosed with was hereditary. At the time I remember being asked if my sample could be used to aid the type of research the OP talks about and I agreed to it.
A couple of years ago, I think 23 And Me was bought out by Virgin Healthcare, at that point I asked them to destroy all my data was worried about it being used to increase the cost of or preclude health insurance.