Back in the olden days, when dinosaurs ruled the earth and before the settlers in North America cut down all the rain forests, the only way to add variable choke to a short barrel was to put on a PolyChoke. I saw that done a couple of times by people who wanted choke on a short shotgun, but couldn't find a short factory fixed choke barrel.
Then along came folks like Ralph Walker, my gunsmith (Selma, AL) when I was a kid. Ralph did a certain amount of jug chokes in shortened shotguns, but he was really switched on by the advent of choke tubes.
Choke tubes were pretty much it for a while. But they do have their drawbacks. They are another complication, one more thing to worry about having something go wrong with. Chances are that with a good installation, good quality choke tubes suited to the installation, proper maintenance and lubrication by the user that nothing bad will happen with choke tubes in a working shotgun. But there's still that niggle in the back of the mind, that something might go wrong.
I've had choke tubes installed in several 18-20" barrels over the years. And had a couple of companies do the work, mostly Colonial because when I was doing most of my experimenting they were still doing business in Selma (now they've moved to Bay Minette). And I've never had a bit of a problem with choke tubes in an 870 barrel, so far. I don't really expect to have problems, either. (But there's still those horror stories I've heard...)
Now that Remington has 18.5" RS barrels pretty widely available, with tritium sight inserts even, to go along with the fixed factory MOD choke, there's another option available. I figured with the advent of FliteControl buckshot, a CYL bore would be all I'd ever need again. I was set, and didn't have to worry about all the complications any more (did I mention I like really tight buckshot patterns?)
But then came the ammo shortage - and that fixed MOD choke made a lot of that buy-what-you-can-find buckshot pattern a lot better. So here we are with things back up in the air again.
And choke tubes might well be some help with all that...