I need some schooling/advice...
The reason for the “flat” EQ’s are due to phase errors, when you start playing with the EQ, you also change the phase in the audio signal. Another reason is the theory of less is more; this simply means that fewer electric components the in the sound path, the better/cleaner signal you will get. Adding an EQ to the signal chain also means adding a lot more components, so less clean sound.
I believe it was in the late 70’s when manufactures started to add a Source Direct switch on there higher end models, this switch removes the EQ circuits from the audio signal path to give you the best possible signal.
This brings us to the next and second most important rule; What ever works!
If you have a pair of nice speakers witch sound great when you boost the treble, then this is fine. It might not bring you’re system into the horned group of audiophile super systems, but does it really matter as long as YOU like what you hear?
Another use of the EQ is the survival mode; you remove some of the audio signal to give room for more details in other parts of the signal. A typical thing here is compensating for the room; in my living room the floor has a resonance of between 75 and 80Hz (a wooden floor). This creates a nasty mudded bass, so here there are 2 options. Use an EQ to remove some of the signal in the 75-80Hz area (by the cost of a change in the phase) or change the room’s acoustics.
The phase is important to the sound stage; if you change the phase in the mentioned 75-80Hz area you might experience that when the bass player hits a note in this area, the sound will come from a different location in the sound stage. Instead of coming more from the right speaker it suddenly comes more from the left speaker or even some times it might sound like the bass player is standing behind you (witch sounds cool but is an error, no less).
Sorry I did not pick this up in my first answer.