the friction is not increased that much but when you use a closed bridge more skin is in contact with the cue. Try to play a draw shot with open or closed bridge and you will notice with the open bridge you need less power to get the some result. Probably you are used to use a closed bridge so you don't notice it but again, i really don't see the reason to use a closed bridge. Even with extreme spin i use an open bridge.. But i noticed Allison Fisher now use a closed bridge when she plays pool so i understand it has some advantage.
I use an open bridge for the majority of my shots, but for anything with power, it's a closed bridge - as it is for the majority of the pool playing world I would think.
For me, if i need to the draw the cb and the distance from CB to OB is small, open bridge is fine - and yes it's nice and easy - but that's not because of the bridge, it's because of the distance.
A closed bridge shouldn't be squeezing the shaft, so while technically correct there's more skin touching the shaft - it shouldn't affect the speed the shaft slides through the fingers.