Getting ready to put up the pool and will be bought a Fibropool 120 heater. I have looked at lots of posts and videos about plumbing with PVC but still not confident. I understand the loop will be pool > pump > filter > heater > pool. A lot of setups show valves to bypass the heater. Why would I want to do that if the heater turns off and on as needed to keep the water temp constant? Why would I want valves in other spots along the loop? Is it just for being able to isolate areas for repairs?