I'm fairly mixed about it, personally.
Being able to inspect post and comment history allowed for finding people who are absentmindedly lying, or are otherwise intentionally and persistently abusive. I believe this was the whole original motivation about such a history being available, even.
On the flipside, it does lessen the potency of various avenues of abuse. Some people would get harassed and stalked thanks to this history feature for example, and it trivialized targeted information extraction too. It also allowed for petty censorship, i.e. some subs would auto-ban people who commented in various other subs.
One might also criticize it for being a minor bandaid over a gaping hole. Your username and user avatar you still carry across subs and are not autogenerated. This means that with sufficiently wide scraping, your posts are still perfectly correlatable, collectable, and subscribeable. Within subs, the same applies to your user flair. This has benefits, i.e. it allows you to block users who you identify as inherently malicious, but it also means that all the aforementioned benefits apply only in limited ways.
Trust requires the sharing of information, privacy requires the obfuscation of information - and so I think these concerns run contrary to each other, resulting in the many solutions of the world not committing fully to either, as they are extreme and unrealistic positions in isolation. Difficult world.