I've heard (but never confirmed) that the propellant or some other factor present in the 'air duster' (compressed CO2) cans can be detrimental to non-metalic components (rubber? plastic? wood?) if it condenses on them... but wiping it off is sufficient to avoid issues. Probably not a problem with 'real' steel (this comes from my previous experience with Airsoft stuff). The only relevance I can think of would be things like synthetic stocks, plastic trigger guards, magazine followers, etc...
Because of this I now use real compressed air (bought a portable tank that I refill with my compressor) - great for getting crap out of your gun's nether regions...
/gc.