I don't believe in bouncing out of the hole (not because I'm worried about staying tight but because I don't want to injure myself), but on both the squat and the bench you should lower the weight as fast as you can under control. The longer you take to lower the bar, the weaker you will be.
Secondly, you can stay tight while taking advantage of the stretch reflex. Especially in the bench, it's the tightness in fact that allows you to get a good stretch reflex (a relaxed muscle has to be stretched a lot further to get the same elastic force production). Rather than letting the bounce do work for you and just going limp, work with the stretch reflex which will give you good speed out of the bottom.
If you see a powerlifter going down slowly, it's usually because he can't go any faster due to the supportive gear he's wearing.