I never know what I'm going to find inside a Strat or Tele neck pocket.
Matchbooks, picks, popsicle sticks, all tone killers.
And the gaps created by these shims can cause a "ski slope" over time.
A Strat or Tele should never need a shim if properly set-up.
But as in the case of this Jaquar, the stock mute on the bridge caused it to sit very high.
If a shim is needed it should be made of a hardwood and be tapered.
Before: A pick, packing tape, and shim!

After: Tapered shim made from mahogany. Maple is available also.

Finished. Proper action in spite of the tall bridge.
With no tone loss!