It seems most of the time when people get in vehicles they just rush towards the enemy and get wrecked immediately rather than using it to help the team get situated and gain control of an area.
When I get in a mantis or hog in the beginning of a match, I advance a little, play it slow and hold down a position and wait for enemies to to try to push so I can pick them off and help my teammates get into good positions and i rack up kills & assists this way. But almost every time I get in the gunner seat, we just end up going straight towards the enemy and wrecked immediately.