This is a point I keep making. There are so many ways that your comment can be preserved. Deleting it just makes it harder for a peer user that wasn't already surveilling you to go digging to see what you have typed in the past.
I keep harping on the dangers of false security because it seems that many people that use the Internet do not understand how it all works. I'm not even just adding this info for those deleting their comments but for those thinking this might be a good idea.
Its kinda akin to thinking a VPN make you private. I mean, private from who. You have to trust the VPN provider when you do that. What info do they have on you? Do they keep logs? How do you know they aren't lying to you? This isn't to say you should not use a VPN but a person that thinks they are invisible is in more danger than someone that understand how they are seen and by whom.
Also perfection can be the enemy of the good. I'm not saying deleting comments is pointless. But just be aware that your comments might be preserved by someone so keep you head up and eyes open.