I got alot of kills with my HFC beretta when using it as a sidearm with my vsr-10, but I bought it as a sidearm for my M4, incase I ever ran out of ammo and didn't have time to reload. So far It's done that once, and luckily I was able to switch to the pistol during one game when my M4 broke down

So although it's certainly not necessary, it does make the game more fun, depending on what role your playing.