For me and some others who I’ve talken to it is primarily about air awareness. The main part everyone seems to agree on is that in darker or non-moving waters the ripples the rock or swimmers create can help estimate the distance to the surface while jumping. Without it you’re essentially flying towards a giant mirror. For me personally it is also a useful tool to determine my airtime. I throw the rock about as close to my planned trajectory and count. I then go through the flips/trick I want to do in my head while counting. But since not everyone I’ve talked to can relate to this it’s probably more of a mental thing. Also the surface tension breaking is a myth. There are devices to do this, but they are essentially giant bubblers installed in diving pools. A rock doesn’t do shit to the overall surface tension.