I would imagine they probably throw out the salt they don't use, but I get the point. Whenever I'm rubbing salt/spice on poultry, pretty much anything actually other than veges, I always put the salt/spice in a little glass bowl, then throw away whatever I don't use. OR, I sprinkle with 1 hand and rub in with the other, but you have to be careful doing that and pay strict attention to what you are doing.
In the case of Barry's situation, optimally I would have taken the chicken out and immediately placed it skin side down, washed my hands, then held the chicken with a fork, done the slashes, s & p, and oil, then placed the chicken in the pan, washed my hands, then carried on.
Note I said "optimally" - what would have really happened is that I would have taken the chicken from the pack, placed it skin side up (a la Barry), washed my hands, grabbed the knife, read the instructions to say skin side down, flipped the chicken, washed my hands, picked up the knife, noticed the chicken packaging was in the way, thrown that out, washed my hands, picked up the knife, noticed the chicken wasn't placed right, repositioned the chicken, washed my hands, sliced the chicken, put s & p on, noticed I spilled some on the board, moved the chicken to pick that up, washed my hands, noticed the chicken needed repositioning again, washed my hands, oiled the chicken, then placed the chicken in the pan, then washed my hands, then carried on.
And I'm not even exaggerating.