What is the Difference/Need for "Assignee" versus "Performer" in Checklist Task Configuration

Summary:

When creating a checklist task, the option to add attachments to document records is available, and when selected, there is a need to specify who the attachments are for: if they are for the 1. Performer or 2. the assignee...

I find this offered selection to be confusing because my understanding is the performer is the assignee of the task, by default - unless of course the performer re-assigns the task, in which case the assignee could be a different person than the original default performer, but even then the person that is re-assigned the task is the new assignee/new performer...