When you invite someone to give feedback in Appraisd, they're sent an email immediately. So the nominee will have received an email and may have begun completing the feedback already.
Uninviting someone will prevent them from giving feedback and changing any feedback they've given already.
Any feedback already provided by the nominee will not be deleted – even if you uninvite them.
The nominee will no longer see the invitation to give feedback on their dashboard on Appraisd.
Once uninvited, you can reinvite someone using the usual invitation process. See Changing the feedback that's been given.