Why wear it up?

Something I just don't understand at the moment is why guys wear a collared shirt and do their buttons up all the way to the top. I understand that it must be some "fashionable" thing to do, but due to my little knowledge in the world of fashion, I'm a little bemused by it. 

I see my guy friends out on a Saturday night and most of them look reasonably smartly dressed, until they get to that little top button that they do up. SUCH a pet peeve of mine that I do not find slightly attractive.

Obviously, this post it based solely on my personal opinion, but does anyone out there find it unattractive? Or did I miss the memo about it being the thing to do? Who knows, but when I was having a rant to the family about it last night, Dad did this, (in his farm clothes) and it had to be on here.