Regular foot fins change your kick timing. You feel their kick power happens over a shorter time, near the end of each kick when your knee moves quickly upwards to push the fin backwards. So, with foot flippers, the kick sequence of your knee and hip movements is completely different compared to barefoot swimming. You can feel it. Foot flippers disrupt your overall stroke timing, arms too.
You can also use them to work on your overall stroke timing to improve your freestyle, backstroke and fly. They help you to coordinate your arms and legs properly. For example, you can use their smooth, continuous kick to lengthen your arm strokes and work on your catch.
So now you can have fins that give you extra speed and the correct kick timing!
See related faq about how these fins build your muscle memory correctly.
See all faqs about why hip power fins are the best for swimming.