I like it because I can fit it into my schedule. I try to do it once or twice a week, and get in one 20 mile group ride that keeps a brisk pace and includes one significant climb. Doing that last rising season allowed me to keep pace with some riders who rode 4-5K miles last year but didn't do intervals....I rode about 1,000, and on group rides, we were about even.

I'm a big believer in the short intervals, and it seems that the science backs it up. Even doing just the 20 minute interval session most of this winter (with NO long rides) put me near the front when we did our first 2 hour spring group ride a few weeks ago. So the aerobic efforts were conditioning my aerobic system as well.