An Application Context is activated when selected parts of one or more application are running.
Important: in Android versions after (and including) L, app detection is much less accurate. For some apps it may not work at all, for others it may activate and never deactivate.
Note that services other than the obvious ones may be running. For example, the default Play Music app may have a download service running even when not playing music at a particular time.
This button in no way affects how the context behaves.
When any profiles have application contexts specified, Tasker checks frequently to see if one of those applications has been launched. The default is every 1.5 seconds.
If you would like quicker response, or you suspect this is severely increasing
your battery usage, you can change this value in preferences
Menu / Preferences / Monitor from the main screen).