This is subjective, but I think bass and the kick drum own the bottom end (unless you have a Hammond B3 in the mix!). The bass is somewhat more omni-directional but requires lots of energy (think headroom) to be out there. The mids give it clarity and musical style. I think growl lives in that range too. The treble highs I usually avoid.
Many country groups mix so that the bass just seems to have lows, w/o the mids and highs. Funk needs the lows and the mids. Rock can be just lows or lows & mids. Jazz seems to like some low and some mids with often a more acoustic sounding feel. Hip Hop can go for the ultra lows a lot, often with little else. Pop used to have a 'catchy' bass sound, but I think that is not so much the case? (I am older!). Now it's all about the vocal. Newer groups seem to re-writting the rules again, with sound quality in the mix that feels cheesy, but if it sells... I don't know if this is deliberate?
I hear groups now with successful tunes that a sound engineer from the old school would laugh at, in terms of a good mix and great playing. However, the vocals still have to sound good.
For me, I always set my bass amp on the floor, as i think that helps the tone. I use an amp that I can turn the horn speaker on or off, and I experiment with it. I used to use a cab that had a 15" EV guitar speaker in it, and it really had the 'growl'. However, it blew up! I am back to 1, 2, or 4 10" speakers in the cabs they come in.
I also record music, and often I have to dumb down a great sounding instrument in order to make the whole song sound good. I never compete with the vocals with anything else, never. Also, the conversion to, say, an MP3 format can change the whole thing. One thing I do is master my own songs, and I put that plug in on while mixing down, so I kinda know what the final product will sound like.
There are so many elements involved... We did a small outdoor gig 2 weeks ago where i had to put my bass amp on a deck on the drummers carpet pad and it sounded like crap. At an outdoor gig last week I set it on the the pavement at a street festival and it sounded great, as usual. I still don't know why it sounded bad on the deck.
Rambling on here, time for coffee!