Coil split is useful for neck pickups, as there's more string energy in that slot, so they're not as bright and thin as a split bridge pickup. However, what's much better than coil split is spin-a-split, which lets you dial in as much, or as little, of the 2nd coil as you want, by converting the neck tone pot into a 2nd volume control, but for one coil only. Basically it's unbalanced coils, like the original 1950's PAF's. You can dial the 2nd coil down all the way and still get coil split, but you also get many more options. Wiring diagram on this site.