There is a need to be able to select audio channels. Decent stereo audio is necessary for any quality video and is difficult to achieve without the ability to select audio channels.

If you have audio that for whatever reason is only on the left or right, this can’t be fixed in rush.

Even slightly more professional recording is ruled out. For example, if you recorded two sources of audio in one stereo track (something common in run and gun and smartphone recording, which rush is geared for) and want to be able to hear one or the other at a time it is impossible.