Some defensemen like to pair their turrets together for better area coverage, especially along well-traveled paths to double the chances of taking an enemy down. Sometimes disabling deployable turrets can be more effective than destroying them. Unless the enemy specifically checks on it, they'll have a nonfunctional turret which cannot be replaced with a new one in another location. Since the enemy has a finite amount of turrets and sensors they can use, disabling turrets reduce the resources they'll have available to them to mount a successful defense. If they do repair the turret, you know where it is the next time, which makes it much easier to disable or destroy it.
Mines are a major consideration.
Keep an eye out for satchel charges, too. Some defenders will lay out a pattern of mines and put a satchel charge nearby. When a flag capper gets near the mines he'll detonate the satchel and with it, the entire mine field. If you see a satchel charge on a flag run, your primary concern will be to get rid of it before destroying any other mines. Depending on where the charge is placed, it can take out a bunch of mines along with any nearby turrets, sensors, and defenders.