Some combos have the input jacks and controls on top. It's often easier (lighter weight) to load a head and cab into your vehicle than some combos.
A) A 2x12 with controls on top is easier to fiddle with (from a standing position) than one with controls on the front.
B) Budda, how much does your 4x12 weigh? How much does the JSX head weigh? (70 lbs?) Now, I know they're different amps entirely, but your YCV is what, 60 lbs?
That said, if I had to go un mic'd, I'd want a half stack, if possible, but raising a combo up a foot or two can have a big effect.
Combo vs Head+cab comes down to whichever configuration is better for you, IF you have the option.