I use stashes like I would use a shelf above a workbench - to put things for a few minutes while I clean up. I think it's a nice feature.
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Tags can be deleted and recreated, so they are just like branches and not immutable as some claim.
Same goes for stashes. They are commits which can't be pushed. Stashes could be implemented by creating a new branch and committing both with a generated name.
Am I missing something? Do both things provide more value than they add complexity/things to learn? :)