The practical application, which I haven't seen mentioned here is that QNH gives you your altitude above sea level so you then have to account for the height of ground to figure your clearance. QFE is your height above the airfield itself. Normally only used approaching and in the pattern to take out having to do the arithmetic to calculate pattern altitude. This way, when you're on QFE and the pattern altitude is 800 feet, you can just shoot straight for 800 feet. If you're on QNH at the same airfield, and let's say it's 350 feet MSL, then you have to shoot for 1150 in the pattern.
On another note, I use QFE a lot here in the UK where there is much less variation in ground height. It's much easier to calculate my clearance when doing aerobatics in the local area.
Hope that helps.
Pitts2112