I first started rock climbing in 1977 after starting work at EMS in Hartford, where a bunch of my friends and climbers worked. At some point I tried out ice climbing, and still have my original tool: a Chouinard Alpine Hammer with the bamboo handle, and a trusty 75cm ice axe! Now don't start laughing yet…have a heart! I got some strap on Salewa crampons which I securely fastened to my Galibier Super Guides (which I acquired as the result of a return to EMS) and there I was, scared as hell on every ice climb I tried. Needless to say, I gave up ice climbing for a while. At the time, that Alpine hammer and ice axe really needed a leash, so I attached some 1" tubular webbing and fabricated a leash, which increased my security immensely! I also had a tether on the hammer which always got in the way and created havoc with my attempts to plant it securely into the ice. The hammer is still in my basement, now for a very long time.
When I picked up ice climbing again, but not too seriously, I acquired various tools, honed my systems, tried out lots of leashes, and finally settled upon the Black Diamond Lock Down Leash. I still use it today on my BD Vipers. Several of my partners also use this leash. In my opinion, it is the simplest, easiest to use leash that I have ever used, and find that I can get in and out of it within a couple seconds, all the while giving my weak hands a little relief and security when I am on the steep one. Now when the clip on leashes came out a few years ago and were all the rage, I could not understand why anyone would want to have the leash permanently attached to their wrist while they tried to aim their cold fingers to a little release button while pumped, and then have to re-attach it after putting in some pro. To me it was the "rage du jour" that I did not understand.
So now the "rage du jour" is leash less, and it seems that some folks think it is the best idea since…that clip on leash??? Just joking. I understand that there is a time and place for leashless climbing, and the tools have gotten so good that it can make a lot of sense to climbers who need that style. I generally climb pure ice, so I don't need to be switching hands, putting tools on my shoulder, etc. And that Lock Down leash, so easy to get in and out of, gives me that little extra bit of security that allows me to relax my hand and not fear the dropped tool. When I am mountaineering, my tool is attached to me and I don't have to fear dropping it. Based upon my early days of climbing with a tether, all I can say is that it is much more convenient to climb with my leash than a tether that always seemed to be in the way.
As for beginner climbers, why not give 'em a leash? Then they won't be dropping their tools unnecessarily, and as they develop skill, strength, endurance, and maybe an interest in continuing the sport, they can decide for themselves if a leash makes sense.
This is just some food for thought, in a sport where everyone should experiment and develop a system that works best for themselves.