I've worked out for many years at school gyms, YMCAs, work-supplied facilities, recreation centers, and health clubs. At every facility there was a certain etiquette. People didn't sit on machines or benches when they weren't using them, except for the clueless New Year's resolution types who rarely lasted more than two weeks. Guys were open to allowing someone else to work in with them (I met a number of friends that way). Cameras were never brought into the facility. And people kept their workout a safe distance from others.
I cannot definitely state when things changed because different clubs have slightly different cultures, but perhaps it was five years ago. Now it is common to see hipsters sitting on machines or benches while checking messages or texting. They are completely oblivious to the fact that they are preventing someone else from using the equipment.
In the days before smart phones, taking video or a photo of someone was difficult because the devices were relatively large and cumbersome. But now, all someone needs to do is aim their smart phone at an unsuspecting person as Playboy bimbo Dani Mathers did to an older woman. Since the new year, a sign was posted to the effect that videotaping or photography in the locker room is not allowed. I would have thought that such behavior was contrary to common sense, but Glassholes have already demonstrated their lack of same via their use of Google Glass, essentially a smart phone integrated into glasses, to capture video of anyone at any time. Some enlightened bars and restaurants have banned the use of Glass and similar products.
In previous years if someone wanted circuit training, i.e. exercise involving weights while keeping one's pulse near a certain target rate, he would use a machine, then run up and down the stairs, use another machine, etc. Some people used jump ropes, but they always moved to a corner of the club so to not injure others. But now a few self-important youngsters are using a machine and then jumping rope without moving away from the machine they just used. Just the other day I saw a narcissist do this without looking behind him, with the jump rope swinging about one foot from another guy's head, with the second guy moving his head to increase the distance between himself and the rope. I would not have been so gracious.
There are signs in the health club notifying people that gym bags are not allowed in the areas with machines. I used to think the purpose of the signs was to forestall the dishonest from placing gym equipment in their bag and absconding with it, but now I realize there is another reason. Some selfish cretins simply drop their gym bags on top of equipment, preventing anyone else from using it. Usually this takes the form of dropping bags on top of benches or machines where the user needs to lie down on top of a padded surface.
It used to be exceedingly rare to see someone monopolizing multiple machines. Now that behavior is seen every day, with these pompous persons dropping a towel on one machine, a water bottle on another, and another item on a third machine, marking their territory like a dog on a walk. And it's not just guys, as women do it too. I try to avoid the machines being monopolized as long as I can, but I can only wait so long. If I need to use one of "their" machines, I simply push their property onto the floor. If they complain, I inform them that it's not their private gym or that they were actually trespassing on "my" machine. If everyone monopolized three machines, the maximum number of people a health club could accommodate would be 1/3 the number of machines, excluding the cardio machines.