The compressor map is useful to help you pick a correctly sized turbo.
Once the turbo is on the car, it is mostly useful to make sure you are not exceeding the manufacturer specs (which most people are doing anyway when tuning).

If it's already fitted to the car, then just boost until it stops making power or you hit some sort of component limit... then depending how the car is used, back down an amount, to leave a margin (less boost = more timing, less EGT, lower IAT).

Also, the compressor map shows how efficiently the compressor can compress air at which flow and pressure ratio and that's pretty much it.
Why you put fuel type into the discussion is beyond me.