Macro interference

Specifically, if you have a Worksheet Change Event handler and that event handler makes changes on the sheet, you should bracket the change(s) with ApplicatiionEnableEvents = False and ApplicatiionEnableEvents = True.

Similarly, if you have a Selection Change Event handler, and you select cell(s) within it, same rules.

In the worst case, it can cause a loop. Best case, it will fire more often than it needs to.