If you are at death's door - you don't need another cactus.
(Oh boy, I've said it now).
When I die I hope that my cacti are the only prickly problems my survivors have to deal with! And when I'm waiting to die, I think plants and flowers would be just as welcome as the people I love. So I say, "Bring 'em on!"
With that in mind, there is NEVER a time you don't need another cactus!!!!!
Just not one needlessly dug up from the wild.