The Sapper is the stock PDA weapon for the Agent. It saps a building which disables their function and rapidly deals 25 damage per second. If a sentry is sapped, it gives the sentry gun a +33% damage resistance from the Agent who applied it to give mechanics a chance to fight back. Despite this shooting at the sapped building with your Revolver is a good idea as it destroys a building faster. However, it is a good idea to not sap the building beforehand. You could break your disguise and have the sentry shoot the mechanic, or take health from a dispenser an use a teleporter to get to an exit before sapping. These small tasks can help you perform better in battle. Overall a sapped building is key to allowing your team victory especially sentry guns and teleporters as it forces the enemy team to work more hastily, but sometimes you shouldn't sap a building for its benefits can aid you.