When a profile contains multiple contexts, power is saved by only monitoring for changes in order of the least-power-hungry first. For example, in a profile with a Time and App context, Tasker will not decide that it needs to monitor for a changing application unless the Time context is active (because the profile cannot become active until both contexts are active).
Tasker rates contexts for power-hungriness in the following (ascending) order:
Items at the bottom of the list won't become eligible for monitoring until all items further up the list are active.
Menu / Prefs / Monitorfor the frequency and maximum duration of these checks.