That's the sort of thing that's covered in a coordination study. It's hard to coordinate a panelboard with non-adjustable breakers, though.
A co-ordination study is part of the design of ANY electrical installation.
Sure, you could use the main breaker, to protect the whole installation, from the last light back to the main, but the cable sizes are not the same.
Most electricians I know, rate the protection to the size of the cable, this gets smaller as the circuits head away from the main breaker and at sub-boards.
After all, you are protecting the cables on "that part of the circuit, forward".
It is a cascading thing.
I disagree that it is hard to effect co-ordination with Non-adjustable CB's, most of what we have here are just that and they are set to protect given sizes of cable, not the loads likely to be carried by them, especially where that could affect the integrity of them cables.
