Priority 1 - Emergency use only, or Stuff you, as a Gnoministrator want to have hauled RIGHT NOW (Note: this will still not call the gnomes that have "Something better to do" to hauling.)
    Priority 2 - Stuff you want to haul right after the Emergency, but is not as important for you so you do not have to micromanage it and set it to 1 after the emergency is done
    Priority 3 - Normal hauling task of the highest priority. This is the first Priority you set, and never change again for several seasons. Examples are Bandages (you really want them at the gate, more than food and drink).
    Priority 4 - Hauling of finished products. This will ensure that your gnomes will empty out workplaces as soon as possible (after bandages are supplied, and the emergency tasks are finished). These are pretty much set and forget.
    Priority 5 - All other Stockpiles - raw materials, corpses (unless you want your spoils on display as soon as possible).
    Priority 6 and below - I never use that. People who create "overflow stockpiles" might use them, or dirt stockpiles. If all other jobs are done, haul dirt, basically.