I remember listening to a couple of young players who simply refused to stop the flow by not observing a single rest and I know from personal experience how difficult it is to contend with silence. So why have them?
If they are taken as having as much to do with sound as with silence they may be understood as implicit question marks:
- What is the direction of my anticipated re-taking of sound: up? down?
- If no change, i.e., if I am to re-enter on the same pitch I just left have I actually rested, or does the rest indicate an interrupted long note?
- Does the rest coincide with the end of a phrase, or not?
- Am I supposed to keep the beat during the rest, or to lose track of it? How do I know?