It really depends on the terrain and trees available in your area. In KS, we don't have too many really tall trees, and it's a crap shoot whether you trust a hollow cottonwood (one of our few common tall tree species). Hanging yourself 30ft high in a hedge tree doesn't make sense, as you won't find many of them that tall, nor with heavy enough masts to hold you up there, and if you did, you wouldn't be able to see the ground for all of the limbs.
I've had stands that were 10ft high, and some that were 30+. I hung one last year that was at the bottom of a ravine, but if you climbed high enough, would put you about 25ft over-looking a heavily traveled trail. 40ft climb to get 25ft above my target.
On average I like to be above 15ft where possible.