Trimming up long feathery skirts that get tangled and dirty is OK but can spoil the dog's look. Shaving is said to NOT be cooler and NOT reduce shedding. My neighbour shaves his GR and says it is so both and insists there is less hair in the house.
Shaving is said to increase heating by removing protective insulation and to ruin coat, that comes back in thick and matted, and impair the guard coat. Certainly another neighbour's shaved GR is a messy mass of thick tangled undercoat and they haven't shaved her now in years.