I generally like to get in and out of the gym as fast as possible. I don't like to hang around and chat (not that there's anyone at my gym to chat with at 5:30 a.m.). And I don't like to dilly dally too much between sets or in the middle of a workout. Fast is the name of the game for me.
But, there are certain exercises - like those aimed at building muscle - where you'll actually get more benefit from taking the tortoise slow-and-steady route. It has to do with the amount of time that your muscles are under tension. And while I like lifting and generally try to take a slow and steady pace (both up and down - using gravity is cheating!) while maintaining good form, that can also get boring sometimes. So, I mix sets of slower, muscle building moves with faster, cardio-focused exercises to get a great full body workout and keep my boredom at bay.
As always, make sure that you're using a weight for each exercise that is challenging, but will still allow you to maintain good form throughout the entire set.