mumsnet advice has always been - if you don't get your preferred choice, you still need to accept the offer. If you don't then the local authority has fulfilled its obligations to you and had no further responsibility to find a place for you. You can accept the unwanted offer and still appeal/go on waiting lists.
however on the parent portal for our LA it clearly says:
"Please indicate below whether you intend to accept the offer. Please only accept the offer if you do not want to choose waiting list or appeal for your other preference choices "
This isn't relevant for me as we got our first choice but is this misleading instructions that could cause a lot of families serious problems down the line?