When you are packing for a tour, do you weigh your gear?
I know of some people who get kitchen scales and weigh everything that goes into the bag individually, and then tally up the whole lot. In one person's case, it was extremely important to do this because he had a very tight baggage limit on the airline he was flying with. He really had to travel light!
I pack everything ... remove quite a bit of it because I realize I'm carrying way too much ... settle on the precise items I want to bring and figure I've got a reasonably high chance of using ... and then weigh each packed pannier or bag.
In my case, I need the total weight for bicycle + bags to be under 70 lbs, or I won't get it up any hills. So for me, weighing the lot is an important part of packing.
EDIT: I'd actually really like to figure out a way to get it all under 60 lbs (bicycle + gear) so that hauling in and out of hostels, trains, and planes is an easier task. But .... it isn't easy getting rid of that last 10 lbs.