When should you reset PRAM and SMC on a Mac?

How to actually do them on an Intel Mac, since that's the bit everyone forgets: NVRAM: shut down, turn it on and right away hold Option+Cmd+P+R for about 20 seconds, then let go. SMC on a Mac with the T2 chip (most 2018-2020 models): shut down, hold Control + Option + Shift (right Shift) for 7 seconds, then also hold power for another 7, let go, wait a few seconds and turn it on. Older Macs have a slightly different key combo.

First thing, check which Mac you have. Apple silicon (M1 and later) doesn't have an SMC or PRAM reset you can do by hand. A full shut down, wait half a minute, start it again, covers both. On Intel Macs: NVRAM/PRAM for the small settings that won't stick: volume, display resolution, picking the wrong startup disk, time zone oddities. SMC for power and hardware behaviour: fans running flat out for no reason, battery not charging, won't wake from sleep, keyboard backlight or ports acting up. Neither one fixes slow performance or app crashes, so I wouldn't do them as a general cure.