Internally, Tasker does its best to keep power usage down. Following are some macro-strategies to achieve this.

Context Monitoring

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.

Display-Off Checks

When the display is off, all necessary 'active' checks (GPS/Net Location, Wifi Near, App) are done at the same time so that the device is awake for as short a time as possible. See Display Off Timings in Menu / Prefs / Monitor for the frequency and maximum duration of these checks.