Reinstall a computer - move to collection or delete ?

I have a very basic question, but can't seem to find an answer for it.

If we install a new computer through sccm, then it picks up the task sequence from the unknown collection.

But what to do if we need to reinstall the machine, after the user has left the company or just because it needs to be reinstalled (windows issues) or he needs to have an upgrade from windows 8 to 10

do we delete the computer from sccm, so it is again an unknown computer or do i create a new collection called something like reinstall and deploy the same tasksequence i did to the unknown collection, so we do not need to delete the computer from sccm.

so basicly Delete the computer from sccm or make a collection.

and why ?