What would you do differently mastering for a CD versus Spotify?
(I'm in the middle of releasing an album, and we don't have different masters for these, but I could imagine that the situation is different for more professional groups)
Spotify compresses it anyway but for digital audio you'd want to encode in 48 kHZ/24 bit whereas CD only supports 44.1 kHZ/16 bit. Anyone who can hear the difference would be an exceptional listener with an exceptional sound system though, at least assuming the masters are generated with proper dithering.
(I'm in the middle of releasing an album, and we don't have different masters for these, but I could imagine that the situation is different for more professional groups)