I prefer leaving skill rust off for the simple reason that it becomes irritating to maintain every skill during periods where that skill is not really applicable, thus just forcing me to waste time setting up artificial situations to “train” a skill my character has already mastered just so I don’t forget how to, say, change a tire or whatnot just because my car has sat undamaged for a week or two.
And yes, there’s the IntCap setting, which is a fine compromise, but I’ve more than once found reason to stop training a skill at a percentage for whatever reason. If I cannot find time to get back to it for a couple of days (say I had to manage an emergency food shortage after dealing with an unexpected wandering NPC stealing my stuff, or had to fight a running battle through a town because I attracted a monster I didn’t intend to and it took a day or two to be able to get back to my base and get set up again), I do not care to start all over and lose all that effort.
Or, heaven forbid, I forget how to make clothes because I spent a day cooking. With the new system for skillups requiring you to make high end items to increase high end skills, I don’t think I relish the idea of trying to maintain a bunch of skills at decent levels once the basics are done. And God help the person who suggests I should rebuild an entire shelter to relearn how to put up a wall or something.
In short… it’s less fun for me, so I turn it off.
Other people like the feature, so hey, great, I’m glad it’s there, but I’m more glad I can turn it off so it won’t bother me.