The One Man Army perk is perfect for people who camp.
The perk allows you to switch your class mid-game to another class.

At first, I thought OMA was stupid because I could switch classes when I die.

However, I realized that you could use OMA to switch to the class with OMA and basically have an endless supply of bullets and never have to move.

For example, I find a could spot to camp. I plant a claymore to block one entrance. I then use one man army to refresh the class and I have another claymore that i can plant at another door. As I kill enemies and run out of ammo, my previous tendency would be to risk going downstairs to make a dash for another gun. With One Man Army, I just switch back to same class I am using with a full restock of Ammo.

The think is that One Man Army replaces your secondary weapon so you've got to make sure you kill enemies before they get too close and you think of switching to your secondary weapon.