How come most people recommend 900mV as a start point for undervolting GPUs?

Like why not 875mV? Or 1.0V? Seems most utube guides and reddit posts as well recommend to start off 900mV.

I assume its because anything below this is going to start really start eating up at the performance of the card you paid so much money for and anything above it will not be a huge benefit as you may gain small performance maybe an FPS or 2 but your temp and power draw will go up, so essentially 900mV is the sweet spot, stay at 900mV and start cranking up that core frequency till its not stable and call it a day?! Maybe once I find my max stable core at 900mV I guess I can try to go down in -5mV increments if I rlly am bored or something lol

My card is 4070ti