In reply to richprideaux
It's not just the better balance, fore and aft, but the weight of the bags themselves. I started with a rack and 20 litre panniers, the combination was 2kg empty. I've ended up with an Alpkit 13 litre dry bag on the handlebars (350 grammes) and an Apidura 13 litre saddle bag (another 350g).
With all the weight at the back back, if you fall to the ground and are still clipped in, it can be a right bugger to unclip the foot under the bike.