Speedy interval sessions require rest between repetitions–and especially when you’re pushing your limits, the natural instinct may be to stop and put your hands on your knees while you catch your breath. But experience teaches us a counterintuitive lesson: Gentle jogging during those precious snippets of recovery sometimes makes it easier to run fast on the next rep. That’s because jogging keeps more blood flowing through your legs, clearing away the metabolic waste products that build up during hard running and contribute to muscle fatigue.
Source: How to Recover Between Intervals
The information applies to most physical activities. The article is on a running-centric website, but mentions the study of cyclists. This should be applicable to swimming… I look forward to updating my training, once my rib heals.