A good grip will help your wrists activate in the golf swing correctly and will add power, distance and accuracy to your swing.
A tension filled grip, especially from having the shaft too much in your palms, will kill your entire swing. It stops your wrists from hinging naturally and then works its way up your arms and into your shoulders and locks up your entire swing.
The width of your legs in your set up is important because it allows for the legs to function properly so that your right thigh can catch up to your left thigh creating the correct downswing and allowing for increased power