Players usually allow control of the playlist behavior, such as looping. I might want to play only 1 at a time and stop (and pressing Next would start playing the next item), or play one at a time in a loop (again pressing Next would jump to the next item in the playlist), or to play the whole playlist in one go and then stop, or to play the whole playlist in a loop. These controls are particularly important with the "playlist auto-load files in the same dir" feature.