Using the foam roller for Iliotibial band tightness can be very effective to relieve pain and tightness, especially outside the knee.
This tightness can manifest as ITB Syndrome, a pain on the outside of the knee and is common in runners who increase their mileage suddenly.
This seems to happen because that tightness causes the tendon that attaches the band below the knee causes friction against the bony structures of the knee. Dealing with whatever is causing that tension usually resolves this and, if you deal with it promptly or prevent it in the first place usually resolves this fairly easily.
The issue may be with the ITB itself or the muscles that act on the band, namely some fibres of the glutes or the Tensor Fasciae Latae. Dealing with tightness in any of these areas can be a very quick fix.