I've been using a front bag for 10 years or so. It eliminates wasted effort spent leaning forward to keep the backpack in balance. I also like having all of my handy things.....handy.

Sacks used by paper delivery persons are a good example.

Here's a link showing how I use the front bag.

http://www.backpacking.net/makegear.html

You'll need to scroll down to see the updated version. Loof for DJs frame pack.