For Mastodon? I need to:
- pick a server and remember it (I've actually lost my own handle a couple of times between months of giving it a try!)
- manually copy-paste the handles of people I want to follow back on my server, since there is no native single-click way to just follow an account I am looking at on my own server
- do the same on mobile, because all Mastodon apps can't possibly be associated with all server URLs on iOS and Android
- remember to follow people I care about, since otherwise there is no way to discover interesting posts outside my bubble
- give up on the idea of global search entirely, which is one of the things I miss most from Twitter: "flight delays XYZ", "MTA line X delay", "<bandname> <cityname>" would allow me to find content by people about any topic of interest in a way that web searches don't.
All of these are annoying but doable for me, but I wouldn't be surprised if they're a major deterrent for many non-sophisticated users.