This article from the Apple Knowledge Base: Reset the System Management Controller (SMC) on your Mac
describes very well which kinds of events are symptoms which might be related to an SMC in need of a reset. But the relationship isn't clearly established.
Is there any simple method to diagnose clearly the SMC state:
- is it OK?
- does it need a reset?
Something like (for NVRAM):
nvram -p | diff /etc/nvram.backup -