I think @sajawikio has it right - the per-trigger "Stop task" option allows you to set multiple triggers which each have their own maximum runtime allowance, where the option on the Settings tab globally applies to all instances of the task.
Example: On one task, I have multiple triggers set. One is to run every Monday at midnight, the other is to run every Thursday at midnight. There's two ways (there's really more, but we're only using the "stop the task..." option here) I could set up the task so that there's never an overlap.
I could set the whole task (under the Settings tab) to have a maximum run-time of 3 days. This prevents task overlapping in the simplest way.
I could set the maximum run-times separately (in the Trigger dialog) for each task. The Monday task would be set to 3 days, and the Thursday task would be set to 4. This gives the Thursday task an extra day to run (should it be needed) while still preventing overlaps.
What would happen if this option is set in both the Triggers screen and the Settings tab? This would require some testing, but there's three possibilities:
- Per-trigger options override the global option entirely.
- A global option overrides the per-trigger options entirely.
- The shortest duration set for the current task wins.
I checked the Help file, and didn't see any clarification on this. To make your tasks perform in a reliable and predictable manner, I suggest you choose one method or the other - never use both together.