It is generally used to reduce the extreme channel separation often featured in early stereo recordings (e.g., where instruments are panned entirely on one side or the other), or to make audio played through headphones sound more natural, as when listening to a pair of external speakers.
Many audio player programs for computers can perform crossfeed via plug-ins or built-in processing.
In headphones, this crossfeed does not occur, so the resulting stereo image is different from what is heard from speakers.
The intent to produce speaker-like sound in headphones distinguishes crossfeed from the more general concept of stereo width reduction, which involves similar techniques.
A digital, or DSP-type, crossfeed is typically more sophisticated, mixing an amount of signal from one channel to the other, delaying the signal to mimic interaural time differences and applying other characteristics of head-related transfer functions (HRTFs) to mimic the changes between the left and right ears.