Yea I know... shadowboxing with weights doesnt really make too much sense... to me atleast.

The only possible benefit I see as you mentioned as well, is conditioning your arms to keep em up throughout a fight, thats why I figured, use gloves while shadowboxing instead of weights (for those that are obsessed with the idea of doing so).

I never thought about using weight while laying on a bench and throwing out shots... might try that one out

For strength conditioning, I usually just use methods like laying down and tossing a medicine balll up in the air and catching it over and over again, annd clap push-ups etc.