what exactly does it do and how does it affect the culture of tumblr
Until recently, blocking a user just removed your ability to see what they did, meaning they could reply to and like your posts and you'd just never get notified. Recently tumblr changed it so blocking makes it so a given user can't see what you have posted or liked, meaning on mass a fandom/group could blacklist users from said group or fandom if they had enough individuals putting that person on ignore.
Honestly, I wish this wasn't true. Like it could be good if it was just used for sharing pictures and cute videos. I stopped following a lot of the blogs that were posting that garbage, the problem is that you never know when you're going to get one of THOSE blogs. A lot of fandoms are unsuspectingly super SJW so it just leaks into everything. What does a blog about birds or pokemon or homestuck or steven universe have anything meaningful to say about fucking anything other than their respective fandom? Yeah, I'm just gonna look at bpd-gem to get peer reviewed studies on the subject of self diagnosing...Tumblr sucks and anything that fucks it up more to the point people leave it is a good thing. Leave this toxic waste dump for the scumbags.