Perhaps souls have an expiration date and go bad if they're not reaped properly.
I used to watch a TV show called Dead Like Me. In that one the FL became a reaper after she was killed by a toilet seat from the deorbiting Mir space station. (The other reapers nicknamed her Toilet Seat Girl.) Reapers had to collect a secret quota of souls then they could move on, and the last soul reaped would then take their place. (Reapers had to earn a living in the human world so the FL got a day job at Happy Time Temporary Services, an amusing name for a fairly depressing workplace.)
The FL's reaper team was tasked with reaping the souls of those about to die in an accident. When the FL saved a child instead of reaping her the child's soul began to degrade and corrupt (if I remember correctly from 20+ years ago) until she sadly walked the child's soul to the afterlife.
Leads were Ellen Muth and Mandy Patinkin.