How to determine high boost vs low boost?

In the course it lists suggested AFRs for "low boost" and "high boost", but what might be low boost in one application might be high boost in another.

How do you determine what the correct breakpoints are? Do you require EGT to determine this? Are there clues we can look to in order to help us determine the correct target AFR especially in boost?

Thanks.

What engine, what mods, what ECU?