I use EQ to subtract and add, ie notch out a mid honk from a honky cab, or to add back what's scooped out from a J or PJ, having both a 4 band and a sweep for the centers on the low mid & high mid, and you can have both of the above. So many useful sounds are possible notching an otherwise smooth or even pretty flat overall EQ. A 3 band gives you less option for a notch you just have to settle for scoop.
On the other hand, so many classic amps accomplish tone that's hard for you to not find something usable with 'only' 3. And the B15 is only 2 band, luckily you'll never hear that amp on a recording though.
On the other hand, so many classic amps accomplish tone that's hard for you to not find something usable with 'only' 3. And the B15 is only 2 band, luckily you'll never hear that amp on a recording though.