To clarify the TL/DR above, you can use dispersion twice during PI IF you are struggling to reach 3rd torrent. Essentially it gives you 6 seconds off the CD for torrent. Of course it's a slight DPS loss, but dying before 3rd torrent is also a DPS loss. Additionally you need to make sure you pop it soon after your first torrent otherwise it won't be up when you need it later on in voidform. You also don't want to use it during PI, ideally immediately after it ends after you've exhausted your SW: D and casting MB would kill you. It just buys you some time.
Blessed Dawnlight neck, grants 30 insanity on use (75 in StM).