PowerCranks™ were originally designed as a tool to help cyclists. They were seen as a tool that could help the rider to better "pedal in circles". From that initial concept we had no idea how good a tool they really could be and how useful they could be to other athletes. But, it wasn't long before we started receiving reports that the benefits for athletes extended far and wide. Major benefits for the swimmer include improved core strength and endurance to allow for a stronger kick maintained for a longer period.
Since the lower extremities play a much smaller role in swimming that they do in most other sports we can expect the improvements for the swimmer will be much smaller than those seen by other athletes. That does not mean they cannot be important because the kick does offer some propulsion (more or less depending upon the event) and any improvement is valuable especially at the elite level where even small improvements are significant.
In general, PowerCranks:
1. Increase the muscle mass being trained. This both makes one stronger and better balanced, reducing the risk of injury
2. The potential to greatly increase core strength and endurance (especially the hip flexors), allowing one to have a stronger kick (especially the dolphin kick) with better endurance for better speed that can be sustained longer.
3. The ability to cross train even when there is no pool available.
4. Improved recovery between hard efforts, especially important when many heats must be done before the finals are run.