Invite someone to help build and manage a list with you, not just view it - collaborators can add, edit, and remove wishes the same way you can.
Sharing a list lets people view it and reserve gifts - collaborating goes further: someone you invite can actually help build and manage the list with you, the same way you can.
Once they've joined, a collaborator can add, edit, and remove wishes, and rename the list - everything you can do, except delete the whole list, transfer ownership, or remove another collaborator, which stay owner-only. Anyone on the list can see what changed and who changed it from its Activity view, and undo a recent change if it was a mistake.
A collaborator can leave a list at any time from the same Invite dialog, and the owner can hand ownership over to any collaborator if they'd rather someone else take over.
A collaborator can add, edit, and remove wishes and rename the list - the same as you can. Someone who only has the share link can view it and reserve or donate to wishes, nothing more.
Yes - open the Invite dialog, find them under Collaborators, and choose Remove from their options menu. They lose access immediately.
Yes - open the list's Activity view to see recent changes and undo one if it was a mistake.