Ok, thats a really good question
Well typically a sniper in airsoft gathers intelligence and passes it on down. Your binoculars will help you do that, allowing you to see where the enemy appears to moving too, numbers etc. Typically we play with radios and if your group does too this is a great addition to your kit.
Generally speaking you want to try to take a flank when supporting an assault keeping opfor pinned down and unable to move or effectively return fire while your team manuvers. Being higher up obviously helps with this as well. But as a sniper lacks rate of fire and there generally is a MED (medium engagement distance) when using a sniper rifle you need a side arm. Strictly speaking a snipers primary is his pistol and his rifle is his secondary. Without a sidearm you are pretty much at the mercy of anyone who enters your MED.