After some research, I discovered the following:
- If the recipient is online then the meeting automatically shows as tentative, to stop someone else booking the same time.
- If they are not online then they can return to their desk, open Outlook and see one or more meeting requests all at once and decide there and then which to accept and which to reject.
- The default behavior as mentioned above is Tentative. But a person can set it on their Outlook application to auto accept all meetings. This is a bad idea though as people may assume a booking and then when you decide to reject it it will annoy them. In effect, you gave your commitment immediately and then let them down. At least "Tentative" means you had not confirmed it yet.