Few guitars have usable coil splits - unless you're looking for thin, dinky, knifey tones. But when a guitar's pickups and switching are engineered for decent-to-good single modes, I use them - a lot.
Electra-Westone guitars of the early-to-mid 80s, their proprietary Matsumoku "Unbalanced Coil" pickups, spoiled me with their exceptionally full single-coil character. As a consequence, I haven't had to chase every splittable humbucker since. For years the Electra/Westones sufficed - and then I escaped the terrible hegemony of humbuckers in geneal to the diverse lands of P90s, Dynasonics, and Filter'Trons (or straight-up genuine original singles) and had no need for fakey splittabuckers.
But you're presumably asking about splittable PRS pickups. I presently have a dozen-plus assorted PRSeseses with splits. On the SEs with 85/15s, I find the splits more usable than the average in the industry - if I back tone down to 3-6 on the dial. And, oddly, the single-coil modes work better with dirt than clean. And, yes, I use them. I wouldn't have bought the guitars just to get those tones, and they could rarely stand alone or become home base (though the neck pickup in single-coil comes close). But the capability is a nice bonus, a useful utility, and another factor in the SE value equation.
The best of the PRS splits, for my ear, are 58/15s in a Core McCarty and the "TCI" pickups in the SE Paul's Guitar. (I'm sure the Core Pauls are even better, just haven't had the pleasure - and I spect the other Core narrow-coil designs excel as well.) On those guitars, the single-coil settings are more than just usable or handy for variety - they're great tones in their own right. Pretty much as big and "authentic" as the old Electra/Westone UBC 'buckers of the 80s. (And probably a bit more refined and dynamic, as the E-W pickups had ceramic magnets which could tend to harshness, rather than good ol' AlNiCo.)