I've heard that dents come back
Dents do not come back, ever! We are encouraging the metal back to its original position. It wants to be there because metal does, just like you’ve heard, have a memory. What it remembers though, is the shape that is was given in the factory. The dent is the anomaly and therefore easily forgotten when the repair is done properly. The metal would be just as likely to dent itself spontaneously, as it would be to allow a repair to resurface. Once a repair is made and the results, whether they are 90% or 100%, are achieved, they stay that way.
Things that are not used to make a repair
What else do we fix?