A spin being of PRACTICAL USE in the conduct of a flight in a glider? Ah, that is a different question, all right.
Firstly, let me make it plain that I agree, a spin is an aerobatic maneuver, and if you spin on your final turn, it is all too likely to be your final turn.
The point of glider flying altogether is to have fun. Not to get from A to B for a £50 cup of coffee, or to fly some rich owner to his stately hunting box.
And the reason for teaching glider pilots the difference between the spin and the spiral dive, which is useful as the recoveries are rather different, is that gliders soar in thermals, sometimes in numbers and very close together, as many as 20 in one thermal, 2 or 3 at one level, and hopefully all turning in the same direction. At speeds not very far from the stall, when a gust may suddenly tip you into that stall/incipient spin/ full spin.
I remember reading about a Lasham thermal, well populated, where the top glider actually did spin down through the gaggle, which scattered in all directions! no collision, nobody hurt, owing probably to the fact that we all have eyes on stalks while engaging in this bizarre behaviour.
Now let me ask one of our favorite trick questions.
Which is more likely to damage your aircraft? Flying faster than VNE? or
pulling excess G?