Not sure what you mean. I'm on Friendica, and I can follow, reshare and comment on posts from people on other platforms with no problem. I don't need accounts on other servers for this, though I'm sure my interaction with them is limited to whatever Friendica supports. I don't doubt you can do more if you actually get accounts on different systems, but that's a choice you have. I don't think you need to do it if you don't want to.