Well, I guess I should say my setup is probably different than almost all of you. I have 14 taps, two 50# CO2 tanks, and five 20# tanks. I keep the 50s on the walk-in, and I do not want to refill that one due to leaks. The current on I have been using for around 9 years now (yes, well past the hydro, so I will need to get it retested when it needs to be refilled). Because I serve 14, I don't keep the gas connected anyway because a manifold that large is prohibitively expensive.
I also have around 5-6 primary regulators, and multiple secondaries, and a couple of manifolds. With that many fittings, I know I've got leaks. When my setup was smaller, with just a single regulator and manifold, I found all leaks and sealed them up, only to find a leak about a year or two later. Now with so many, I don't have the energy to find all the leaks, so I know I've got leaks. It doesn't matter to me though, because I don't keep the gas on.
The biggest thing I am trying to convey is, a leak only matters if the tank is on. If the tank is off, a big leak will be obvious and easy to fix, and a slow leak won't matter at all. So I prefer to play it safe and turn off the tank, and that is what I recommend to everyone. I know way too many brewers here on this forum and others, as well as in the club that have lost tanks due to leaks because they kept the gas on. If you never want to lose a tank to a leak, don't leave the tank on.