when i sign up for such a platform, i might want to find info/news about the things that interest me. say my hobby is chess. i can (and should!) use some kind of hashtag system to find chess related content, and then i can choose to follow based on that. as for an algorithm, if i've followed 10 people to find more discussions about (x, y, z) then an algorithm might be able to find 10 more people that talk about similar things. i only vaguely remember, as it was about 8 years ago when i started using twitter, but i think it succeeded in recommending me bitcoin/dev related accounts that i wasn't aware of, quite a few times.

if you already know who you want to interact with, sure. but in a case like that there were probably at least 50 accounts of people i "knew" from irc, reddit, mailing lists, conferences w/e that i had no idea were on twitter, let alone their user names.

Isn't that obvious? while i admit, it is *not* obvious, how to do such a recommendation algo "right".