Surely the relevant charts should always be to hand. Ok it depends on the context a little bit - if I am operating from my base aerodrome then I am not obsessed about checking the SSAs on the low level but the principle still applies.
But in particular for descent I feel the low levels should always be available and indeed consulated. Msa on plogs can be incorrectly annotated. I feel that we are getting a generation of pilots now who are too dependent on what the FMC is telling them.
Perhaps in the days before radar environments went we had to give standard position reports there was more awareness of FIR boundaries - you got the handoff when you called at the FIR. But now we are (usually) in a radar environment you have to be more proactive to spot that you havent been handed off to the next sector. Also I feel that an awareness of FIRs is a part of flight planning since the ATC plan shows where the FIRs are.