Everyone has a favorite side arm, be it a revolver or a semi-automatic, from spring to CO2. I happen to run a Green Gas 1911 because it is faster to put Green Gas in a magazine that CO2. Using Green Gas you do have less FPS than CO2 but it is much easier to fill a Green Gas magazine than it is to put a CO2 cartridge in a CO2 magazine.
Pistols allow sniper rifle users to have something much shorter, with a higher rate of fire to use if they run in to a CQB area. Designated marksman rifle (DMR) users also encounter the same problem of their main gun being too long to use effectively in CQB areas. For Assault Rifle users, it allows them something to use as an alternative to reloading. If you are trapped in a room by suppressive fire and need to move quickly, it can be much faster to draw a preloaded and cocked pistol than to reload another magazine. Sub-machine gun (SMG) users won’t usually need to carry a pistol as SMGs are very short and light weight and can fill the position of a pistol. Light machine gun (LMG) users may want to carry a pistol as many LMGs don’t usually have an option for Semi-automatic, and some fields won’t allow full auto in an area that has buildings, even if they are spread out. This makes a pistol advisable for LMG users as well. No matter what you run, it is good to keep a secondary with you, in case your primary weapon fails for any reason.
Pistols are definitely nice to have at an airsoft event because if gives you something to fall back on if for any reason you can’t use your main gun. Many people think that if you have to resort to your secondary that you’re pretty well done for anyway. On the contrary, there have been many occasions when the secondary airsoft guns have help an individual stay in the game and keep the fight going. If you’re playing in a game and your battery dies, you can still turn to your sidearm.
There are also a lot of people who take no rifle and just run a pistol or even two pistols. Usually, when you use a single pistol, or even dual wield, it can make the game more challenging. Some airsoft players really enjoy the challenge of using only pistols against AEG rifles. No matter why you use pistols they can be very effective and useful in almost any airsoft scenario.