'power' is a guess, it's a pretty good guess, but it's a guess. the sampling rate is usually 1x per second. if you're churning out say 85rpm this of course puts the meter in a different spot for each measure which can cause differences in the strain gauge, provided it's crank or pedal based. even if it's a powertap wheel there is still sampling variance. so for that reason most people who train would use something like the 10s or 30s reading to smooth out the irregularities. instant power jumps all over the place and is useless.
so for that since you are looking at an average over time you only need to peridocially look. you will also start to gauge the power very easily. as it is i can pretty accurately predict the feeling of anything under about 500w.
NP lap is super helpful on climbs to make sure you're not going to burn yourself out.
sprintervals it's useless, just turn the crank.
biggest benefit honestly is long efforts and tracking your TSS and TSB