The gist of foam rolling is basically for flexility and muscle elasticity. Flexibility and muscle elasticity is influences by two proprioceptive units; the GTO (golgi tendon organ) and muscle spindles. These are reflexive units.
The GTO is located between muscles and tendons. Essentially this unit let's your brain know how much tension is accumulated during contraction in the muscle. If too much tension is amassed, the GTO will activate and inhibit muscular contraction to protect the muscle from perceived injury.
Spindles on the other hand reside within muscle, running parallel to your muscle fibers. They essentially operate as a protective mechanism against excessive stretch of muscle. When a muscle is suddenly stretched beyond its normal resting length, the muscle spindle fibers can cause reflex contraction of the muscle.
So what's the big deal?
By activating and stretching these units, you can drastically enhance the flexibility of the muscle. Personally, I felt incredibly better after integrating a SMR component into my program.
SMR = self myofascial release. I think I've talked to you about it before?
Foam rolling just happens to be a great way to get this job of activating and stretching done. It's basically a deep tissue massage. Using one is one of the most effective, all-around self-maintenance tools you'll find for releasing tension while improving mobility.
I could go on and on about it but here's an article over at t-nation you should read:
TESTOSTERONE NATION - Feel Better for 10 Bucks
Oh, I should have just kept my mouth shut and searched for articles for you to read, b/c here's another one:
http://www.t-nation.com/readArticle.do?id=1259323
I never was much good at science. I learn new stuff here everyday--sometimes it's even useful. 