[HansW]

It doesn't make much sense to stop on the way to a fate to battle aggroed mobs. You'll never arrive in time for the fate if you do. So this flag controls the bot behaviour when its waiting for a fate to reach the percentage you setup before joining the fate. So if your toon stands around waiting at the edge of a fate, it will defend itself.
It will also not make it attack any non-fate mobs when it joined the fate and when there are fate mobs available. Its rather killing fatemobs instead, even if it dies doing so.