Humbuckers have two coils and when assembled with 4 wires you can send one coil to ground leaving just one coil active and so giving a single coil sound. The problem is that with an 8K pickup you are effectively getting a 4K pickup which may sound thin and create a significant drop in volume. If you have a 13K pickup then a full coil split is OK as you still have 7.5K, Nik Huber and others do this.
The other option, which PRS use a lot with lower power pickups, is to have a partial coil split. Instead of using a solid wire to send one coil to ground a resistor is used instead so that not all of the second coil goes to ground. You still get the single coil sound but you keep enough output to not have a dramatic drop in output volume.
The short answer is if you have pickups below 12-13K + then a partial coil split will give you a better balance when you engage.
