Because it is the only thread I've seen it brought up in without necro'ing old threads, it is good practice to play around with that extra .2-.3 seconds of cast time that still allows you to pull off a spell. This works for any and all castings. Getting the hang of it, I've used it as a PLD while tanking Titan HM to dodge plums when needed and I want to help mitigate something during chaos ensuing from DPS dropping, or Ultima HM as the OT on the MT and healers. While it can seem to be negligible, the little time saved by the above practice can be a lifeline. Especially as a healer.

Just my two cents. Others mentioned it above but I won't quote them as I'm too lazy to do it from my phone.