If people managed to keep the T-bar alive after all these years, I give them a tip of my hat. They have way more pull than I ever could.

The short answer is that it gives you the ability to control the length and execution of your transition without having to come up with a quantifiable number on the fly.

A few examples:

The obituary type story. Need a couple slow dissolves, slower than what's set as your auto transition rate? Use the T-bar. Need a super slow fade to black? Put black in preview and go slowly on the T-bar.

Musical performances: dissolves are much more appropriate for the slow songs and using the T-bar allows you to go with the flow of the song without figuring out a number. The T-bar dissolve tends to feel less linear and less mechanical due to our natural tendency to not want to break off the T-bar on the end stop.

Start dissolve and hold: it's super easy to do with a T-bar. Start pulling and then stop where you want it. It's nice and artsy for musical performances when you have two offset camera shots (like with two different musicians) and want to blend them in for a bit and then fully transition seamlessly.

At the end of the day, there is still art and aesthetics to production, and the T-bar is an appropriate nod to that in a world that is increasingly programmatic.

I feel like trying to mouse a T-bar is asking for trouble, but if it works well for others, who am I to judge. I never thought about the bar snapping back when it finished, but it does strike me as odd now that you mention it.

I set up the slider on my X-touch Mini to work as a T-bar, but I have to remember to run it once before a show or else it does this weird snappy thing where it sort of starts a dissolve and then snaps back to the original source.

Use the Panel Builder, and you will have a "T" Bar that works like any hardware "T" bar.....it stays where you stop and does not snap back....and, it is vertical, like a real "T" Bar...

Why would you want a short cut for a "T" bar?.... a "T" bar should be a manual thing....and if vMix programmers would make the "T" bar react with its effects, I would understand....but you can not select an effect in vmix, and then use the "T" bar to transition, it transitions as soon as you select the effect, which is not how other apps do it....select an effect, and then hit 'auto', or 'take' for the transition to take.....that is where the "T" bar comes in very effective...

I do not use hardware switchers, I use software only, as it is easier for me...

Here is one of my Panel Builder Templates: check the "T" Bar