A common frustration on social media is a near total inability to control the environment in ways that are common in real life, especially in regard to direct interaction.
Effective bad actors can destroy a community that doesn't have a sentry monitoring all interactions every moment of every day for eternity. Many bad actors stifle growth by focusing their attentions on users new to a group such that these new users are discouraged from engaging the community.
The ability to moderate one's own posts and comments can offset these and other factors to very large extent.
If I have the power to completely moderate everything inside my posts, the workload of the sub's moderators will be substantially reduced as I am likely to maintain a discussion that is inline with the sub, as I and others are likely drawn to the sub for purposes of having similar discussions.
It is important to note that the purpose of self-moderation is not specifically to foster lopsided discussions, though that may occur, but rather to foster good discussions where good is from the perspective of most users drawn to the sub.
The same goes holds true on replies to comments.
If the moderation features on replies to posts and comments functioned separately blocking features, it grants users an option to continue interacting with users in other parts of the site that they would otherwise not due to being blocked.
If I make a post about making two different airplane models to appear as close to the real airplanes as possible, and a commenter insists on changing the conversation to be about some technical comparison between the actual two airplanes, I would find this to be highly annoying noise rudely inserted into my conversation. If my only tool to remedy the situation is to block the user, then that is the tool I am going to use. This might be unfortunate, because if on some other sub I want to find the best way to clean my pool, this same user would be able to provide information to me.
I really think a site with self-moderation would be head and shoulders above most other sites I have used.