Actually Access time, I will disagree about the cover thing, and I will give you and allegory as to why.
When I first started playing, I borrowed a pump from one of the gys I played with and he was carrying a 98C with R/T. He had two other comrades and I had one other who had used a Brass Eagle so obviously we were outgunned. I hid beneath a tree branch along the path of the way I knew one of them would go and kept perfectly still, and when he passed by me at about ten feet, I waited...and waited. His two comrades opened fire down below so I popped one in the back of his knee. With the other two having lost their flank security, I got up and moved in behind them and took one out before the other was eliminated by my teammate.
The point of this story is that there are times when you have to split your forces to defeat the opposition, and when you do, you must use every available factor to your advantage. Even if you are fast, somebody can always be faster, and even if they aren't, good anticipation of an agressive player's next move can reduce the advantages of a blitzing like attack plan to zilch. Some guys like to play pump or stock style (even I do once in a while) and when they are faced with guys with semis, well let's face it: you could be in trouble in an outright firefight. Do I think it is sniping? No, I prefer "ambushing," but the concept these guys are talking about is similar.
For as I walk through the Valley Of The Shadow Of Death I fear no evil; For I am the Shadow of Death and evil must fear me.
"Get your facts first, and then you can distort them as much as you please." - Mark Twain