Normally bridge shaving is a kind of sacrilege, I suspect, but sometimes ... it's not all that bad.
There is an assumption (wrongly made) that, for any given acoustic guitar, a bridge's original metrics (size and weight)
ARE perfectly appropriate for that guitar. Replace the word "are" with "might be" and the statement would be accurate.
Knowing the role the bridge plays, and how bridges have been made, selected, and applied to countless guitars across decades and decades by countless craftsmen who operate under completely different understandings allows one to re-examine long-held beliefs.
The bridge, a visible exterior brace on an acoustic guitar, is a
CRITICAL component in determining the sound output, affecting tone as well as volume. At the very least, a given bridge's metrics must (should) be matched to that instruments soundboard for maximum effectiveness (I am referring to a soundboard's material, stiffness, bracing, etc). If it isn't (or wasn't), there may be opportunity for improvement.
A bridge may be too small, too light, too large, too heavy, or be applied in the wrong location.
Shaving a bridge is often done merely to stave off a neck reset. That may or may not be what is best for the sonic output of the guitar in question but it may be the pragmatic approach to keep the instrument playable. Resetting a neck on an instrument whose bridge has been shaved, assuming the now shaved bridge to be under-sized, may call for a new bridge to be applied, one that is properly sized.
Shaving a bridge, as described by Canard, is a perfectly reasonable technique for the reasons described, and may be exactly what a guitar needs.