Indeed. Even a cartridge you think you'll never need can some in handy. Mostly because you're going to need it!

I left a lot of (other people's) 9mm brass on the floor over the years. Then one day, I decided to start loading 9mm.

I despaired for a bit, and considered buying some bulk range brass, and then remembered I had a couple "bucket dump" bags--the bagged contents of brass buckets from the range that were too dirty and mixed to pick through, that I glommed because they had a decent number of the .45s and .38s I was looking for.

So I pulled on a pair of nitrile gloves and went to work. An hour later, I had ~300 pieces of 9mm brass, ready to go. Plus another 100 .45 ACP cases, and half of a dog treat container's worth of mixed .40 and 10mm. Just enough to get started with the 9.

Now, I'd never think about reloading those pipsqueak .380s. But...yeah, I saved them.