Foam rolling or massage?

One reason foam rollers are often used is that most people are not trained to give good massage. For massage to be relaxing, it should not cause pain--because pain causes spasm. A trained massage therapist will be able to sense how much pressure is "too much," but this ability has to be developed over time.

Most people are woefully insensitive to "reading" via touch, and end up causing pain. (There is a nice therapeutic point of pressure in deep-tissue massage that could be referred to as "hurts so good," but this is not considered pain for the purposes of this discussion.

Thinking in terms of simple physics helps us to understand why applying pressure unevenly with a narrow area (such as fingers or the side of the hand) is more likely to cause pain. A foam roller broadens the distribution of pressure so as to dramatically decrease the likelihood of causing pain.

So it's not that foam rolling is better, it's that foam rolling requires less skill. It also simulates the long, effleurage movements that therapists work to perfect. These types of long movements have been shown to increase circulation of blood, leading to decreased spasm and decreased pain due from ischemia. (Though there are better methods to decrease ischemia, this one is easiest and still effective.)

That said, a trained massage therapist is probably going to be better at foam rolling, too, and may do so to save his or her hands some wear and tear. But many therapists prefer not to use devices, as they can assess and apply therapy much more effectively with their hands. Most therapists l've known--and I was certainly one of them--consider these kinds of things a crutch. They work, but they're not ideal.