Because most of these exercises use bodyweight you'll be working multiple muscle groups. When we do lunges, squats, and related exercises we use all of the muscles around the legs and glutes - a perfect combination for efficient exercise, great legs and a great backside to boot!
Stretching is a very important part of an exercise program. The biggest reason being that it keeps the muscles flexible and the joints mobile so when you move (exercise or just moving through life), your body can flow and feels good.
The sun salutation is a a great way to ease the body into movement whether it be the beginning of an exercise session or the beginning of a day. For those that are new to yoga it's a great introduction to the practice because it combines many of the fundamental poses of yoga. In fact, just a few sun salutations per day will take you a long way in your yoga practice.
When doing a sun salutation we stretch and flex all the major muscles in the front and back of the body: The hamstrings and quads, the low back and the belly, the upper back and chest, the upper arms and lats. And, my favorite reason for doing the sun salutation is because we stretch and work the spine in both directions. A sun salutation is a great way to get some major movement and stretching into a very short amount of time. I use sun salutations for warm-ups on a regular basis in my online CoreFit classes (http://powhow.com/videos/Lucis-Studio.)