Question

How would it benefit a cell to possess a sequence of DNA that could be transcribed and then edited into several different mRNA molecules?

Answer 1

It would benefit because multiple proteins could be "spliced" (process in which pre-mRNA cuts out certain sequences, usually introns but also exons, depending on the situation) out of 1 coding sequence- this is part of the reason why the human genome is so small/has so few base pairs. Having a smaller genome would be a benefit since there would be a smaller chance of potentially deleterious mutations that may harm the cell.

This also means that several related proteins could potentially be blocked from transcription (and thus translation). This may be advantageous in certain circumstances when this may be necessary.

Hope this helps!