In the close quarter environment the sidearm is a shooters best friend. A pistol allows the operator to effectively engage any enemy encounter while maintaining mobility throughout tight spaces. Keep in mind this is airsoft while basic firearm rules apply (all guns are loaded, finger off the trigger until your ready to shoot, muzzle control, ensure you know what your shooting and beyond it) some actions can be eliminated from the manual of arms (such as clearing gun jams).
Accuracy
Most people well tell you their sidearm is very accurate even over large distances and some are. Although an average airsoft operators, including myself, have tried engaging a target further than we should. The truth of the matter is that a pistol, shotgun, rubber knife, etc is a close quarter weapon. Keep this in mind when engaging your targets. In these environments it becomes more about putting those bb's on your target -anywhere on your target- rather than a specific location (such as the head, arm, foot).