Midrange is where guitar tone truly lives. Now, this might not apply in certain cases; if your style tends toward super-low tunings and massive metal wallop, chances are your EQ curve looks like a smiley face (ironically enough) and suits you perfectly. If you seek big, bad classic rock or hard rock tones, however, midrange frequencies are definitely your friends. If you think about where a rock band's respective frequencies would be "shelved" for maximum effect, consider that the drum kit takes up a lot of sonic real estate both in the low and high ranges. The bass occupies mostly lows and low mids. The vocals live mostly in the high-midrange area, and that leaves a nice, cozy niche right in the middle (overlapping the bass and vocals to some extent) for the guitar. By sucking out the midrange, you're basically robbing your amp of the strongest part of its voice. That's why metal-oriented rigs that de-emphasize midrange are typically higher-wattage units; they have to compensate with sheer power. You'd be shocked at how loud a little 20-watt tube amp sounds in a band when it's allowed to sing with its own "voice."