Yes, it's definately much easier to play if you have your guitar up high. The only reason to have it hanging low is if you're trying to look cool, I would say. :) Most guitar players with their guitars hanging low (Like Slash and Zakk Wylde) rest the guitar on their knee or something similar when they're playing complicated lead parts.

Barre chords are especially difficult to play with the guitar low (with your index finger barring). If you still want to keep your guitar low I suggest you play barre chords like Jimi Hendrix would do, with your thumb fretting the bass note. I even play power chords like this (with thumb on bass note) sometimes when I'm standing, as I find it much less painful for my wrist.