I wasn't aware of these until recently. Me and my youngest lad go for a game of pool at the weekend. Last weekend we were at Stalyvegas pool hall in Stalybridge. A few teenage lads on an adjoining table all wore them. Seemed to be for carrying those vape things that every time they puff on it is like when they open the doors on Stars In Your Eyes. Also for phone chargers which they don't think twice about plugging in without even asking. I might take a toaster or microwave and plug it in and see if anybody says anything.
Monday we went to Savannah in Whitefield. Two middle aged men both had man bags. I hazarded a guess they might contain spare cue tips, cue cement, sandpaper etc. for emergency tip repairs but they seemed to be for reading glasses, Rennies and Gaviscon.
In both instances I would still say there's enough room in shorts and jeans to carry all this. Handbags and umbrellas are not for real men