This!
A good example is the Eventide H9 (a great pedal, BTW), which has meters expressly in order to 1) Not overload the input, and 2) Send unity gain back to the amp or fx loop. It works well, and it's super easy to achieve unity gain through the H9 effects. In fact it has optional automatic unity gain matching, so if you raise the input level, you can have the pedal set the output gain if you wish.
Helix is very advanced, but the comments about different guitar pickups is true ... they push the inputs in a huge variety of unpredictable ways, and input meters would make it dead simple to avoid clipping, as well as optimize input signal level. I would love (at the very least) input and output meters.
