Originally Posted by
dddc
+1 on the delaying other people. There is a marked delay in gates opening when using a phone app compared to using an Oyster card. If you're going through a major West End station at peak hour you're likely to get people walking into you and your group because they won't be expecting one person to tap a device, let someone in, change cards, tap again etc. The crowds can get pretty big at times at anytime of the day or night.
In my experience, preauthenticating before reaching the gates eliminates a fair bit of the delay (though probably not all of it). However, having to share a device among multiple people could definitely cause a bunch of hassle.