I would never use it, just like I dont delete post I make that make me look stupid, I just feel its a bit immature.
If I go online, I expect to see opinions I disagree with, I expect to have someone insult me at some point and I expect to bested from time to time. That's the fun of it, it mixes things up a bit. Plus there are plenty of users that I have argued with or whose posts I thought were retarded that later on I got along with very well or made a post that gave me a good laugh, if I had just decided to block them, that wouldn't have happened.
I say the only reasonable time to block someone is if they are literally harassing you non-stop. Even then I wouldnt, but I cant expect everyone to hold the same standards, you do you baby boo.