All of my tracks are recorded in 16-bit format. Why should i bother mixing them down to a 24-bit file?

When ever a digital signal passes through a fader, a pan pot, a plug-in, or is summed (mixed) with another signal, its word length is increased. The resultant signal is typically represented as a 32-bit float on most host-based DAWs. (note: a 32-bit float is roughly equivalent to a 24-bit integer.) Those addtional bits contain the vital details of your signal pertinant to the accuracy of the stereo image as well as low level information such as the tails of reverb. Please do not throw those bits away by tracking back to a 16-bit file. Instead, use your application's "bounce" function to properly capture your mix at 24-bits when writing out to disk. Most applications support this type of file rendering. Please consult your owner's manual, online user group, or technical support department of the audio program you are using for more information on how to accomplish this crucial task.