Bridge & Neck pups (any decent ones) inherently have different tone character, just by nature of their position relative to the strings, bridge, etc. possibly different resistance & output levels. This is one of the factors that drives the aftermarket pickup market, and why Seymour Duncan & DiMarzio (just to name 2 mfrs) have so many different models.
With 2 pups & a vol control for each, and with both pups selected (i.e., toggle switch middle position on Strum's Epi Dot, SG, and Ibanez ARC300) you adjust the 'blend' of the 2 pups. If you've got a tone control for each pup, like on the Dot, you really have a range of tones to mess with by varying the relative volumes.
That Ibanez does one peculiar thing: with both pups selected, if you kill the bridge's vol to '0', they both go out. It's like a 'Mute' function.
If you only have a Master Tone (like the Ibz), or Master Volume, then you have no such capability.
Strats ('classic' original wiring scheme) give you a Master Volume, but your tone controls are for the Mid & Neck pups. You get what you get from the Bridge pup, period. What's ususally overlooked with a Strat is that the original concept with the 3-position switch was to choose 1 pup at time, the bridge was for lead work and the other 2 for various rhythm tones. Then somebody found the 2 & 4 'tweener' positions by accident and The Quack from blending parallel coils a bit out of phase was discovered.
I'm getting way OT here...sorry...but the point is: that's why those controls are there. Not just to be dimed for max output.
Volume & tone controls on the guitar are really important when tube amps have no tone controls.