Do all rallies have to be booked?

We have been CC members for over 6 years but have never rallied (only used main sites and CLs) because information in the magazine was too scanty.

After speaking to friends we joined the C&CC and found their magazine rally (etc.) descriptions so much better plus we can just turn up without booking at the vast majority.

Having had that experience it made me think again about attending CC rallies so I just looked at the information on-line and it appears that all rallies have to be booked in advance. Is that the case or are there some where the convenience of just turning up is available?