Does the shop retain right of first refusal, or is moonlighting A-OK?

I’m showing my age a bit, but when I write a car up for a LOF job, while I’m undercar I’m sniffing around looking for spots to hit with my grease gun. Many newer cars have nothing at all, but an older truck? There might be a dozen. Older tractors and motorcycles, which I also service, have grease zerks all over the place. And sometimes, since grease fittings are often neglected these days, the grease will dry up and when you put a gun onto the fitting, grease just squirts all over the place. Has that ever happened to you?
Everything you need to clear a clogged fitting may be right in front of you. Photo by Lemmy.
There are lots of ways to deal with this, of course. Replacing the fitting might work. Some folks smack ‘em with a hammer. (I do not love this.) Other brave souls heat that grease up. Me? I don’t do any of that. I use a trick someone showed me many moons ago that sounds like it shouldn’t work—but does.
Find a rag, the thinner the better; something like a rag cut from an old t-shirt often works well. Spread it over the grease nipple, then shove your grease gun end over the nipple that’s now covered by a rag. (You’ll have to adjust your gun’s collet both going on and coming off, but that just takes a second, of course.) I can’t tell you why this works, but that trick has saved me a walk back from a field more than once.
Give it a whirl! (And if you know why this trick frees up the clog, please let me know; I’ve wondered for years.)
Engine oil is a lubricant, but that’s not what the task’s title is referencing.
Every tech has a story. What’s yours?
What does your shop use? Where are you? Can you help us make a map?