Unfortunately, since it's been a while since the option was added to block someone, and I haven't previously felt the desire to use it, I've forgotten what precisely the effects are. I remember it doesn't seem to work in the fashion people generally expect, but I don't remember in what specific ways those are, or what it actually does do.

I did find the news post from when blocking was added, and it states that blocking someone makes them unable to message you or add you as a friend. Is... that actually all it does?