Everyone loves Savasana, for obvious reasons. The first time you do it in class you've just finished the standing series and are ready for some relaxation, and of course you do it between each posture in the floor series. The teachers make it very clear what the benefits of this posture are, a rest stop, a chance to refuel after each posture, etc. There is one other major benefit that you may not have considered, which I'll discuss in a moment.
Before I get to that, I'll share one of the best pieces of advice a teacher has ever given me. At one point after practicing for a few months, I was still having a very hard time with the floor series. I was really tired and could barely do anything in the floor series. So this teacher told me to get into savasana as fast as possible after each posture. Don't drink water before savasana and don't delay getting right into it. If you need water, go ahead and drink some after savasana and before the next posture. I started following this advice and it made a tremendous difference in my practice. I had more energy and the floor series was much easier to get through. Still not easy and it's harder for me than the standing series, but at least I can DO the postures now.
As for the other benefit of this posture that you may not realize, savasana teaches you to hold a position in space without having to worry about balancing or stretching. The key here is that the power of an individual steps from their ability to hold a position in space. Let that sink in for a second. How does one generate power? By being there comfortably and holding their position in space. The implications are far reaching, from your job to relationships. If you can hold your ground and be there in any situation, you generate power. No one can strike you down, and you can accomplish almost anything - including the floor series:)