Yes, up close, low light issues are arguments for not having a crappy scope. The focal plane is irrelevant to that.
So here is the easiest way I can explain the difference in a practical manor. Let's set a ground rule for either argument.
Miss matching turrets and reticles, is unforgivably stupid. Any focal plane better have the turrets adjustment and reticle match.
FFP strong points:
The reticle is ALWAYS the same size, RELATIVE to the target. So the reticle matches the turrets adjustment at any magnification. Where this shines is for ranging a target, OR engaging and correcting for misses on targets. Especially helpful for coyotes, or deer on the run if you miss. Adjust what you saw you missed by.
SFP strong points:
Shooting VERY high magnification at known targets. Such as paper and 32X. You can keep a very fine Crosss hair, for this bullseye type shooting.