Check the video of this armed robbery to a cell phone store at 00:40. Chubby BG goes for his pocketed gun and takes him forever (5 seconds). Of course unarmed employee can’t do anything but retreat.
Five second is a looong time in a shooting situation. I favor carrying on a holster because your time to reach the gun and respond is much shorter. This video shows a new shooter at an IDPA match and you can tell he does not have a lot of experience but still managed to draw and shoot in about 2.5 seconds.
So, if you Pocket Carry do take in consideration that nasty time lag you will be facing and train accordingly.