I used 5 of those to deck the trem of my Strat clone, as I don't use it and I like my guitars to stay in tune.
This guitar has a thin tremolo block, offering much less inertia than those with more mass. As a result a massive amount of string energy was dissipated by the trem springs. Screwing in the spring claw all the way to the front of the cavity didn't solve the problem, so I decided to deck the trem.
I get quite a bit more sustain that way, as expected. The string vibrations also propagate much more through the wood: I can feel them clearly in the neck now for example, whereas before decking the vibrations were mainly located in the body around the bridge and spring cavity.
For anyone attempting the same operation, remember to mute the springs to limit mechanical noise. I cut lengths of electrical velcro ties the same size as the spring coils, rolled them up with the fuzz facing out and inserted them in the springs before installing them. It works like a charm.