Talk:Expedition/@comment-27796855-20160510130412/@comment-26715360-20160510185143

It roughly has a 50% chance of being triggered for each node you pass through (aside from the aerial battle nodes). That means that if you're lucky, you can actually get pre-boss support on every node before reaching the boss. Of course, that also means that if you're not so lucky, you can get no support at all during a sortie while still having to pay the fuel and ammo cost of the expedition. Sparkling can help increasing this triggering rate, as mentioned in this article.