I'd like to think most of us on here are intelligent, we have proven ability to read and understand text books and pass exams. So we are not stupid, we are capable of making a rational decision based on weather, aircraft serviceability and the state of our health before going flying. Most of us will happily accept that there is logic to supplying information to others about our flight either through a formal or informal process. I see both arguments, I don't book out to go to Tescos but I do want someone to come and look for me if I end up broken somewhere. That is the risk we accept when we go flying.
Maybe 20 years ago an aircraft was not booked out from a local club and it crashed killing the occupants. No formal booking out process was complied with, at that time the club was run informally and did not insist on booking out, although you could argue that merely by booking the aircraft for an hour's slot they had booked out. The occupants would not have been helped had they done so but clearly in the helicopter accident described a couple of posts back it did help.
So we have a risk of an accident, the consequences could be very serious (I happily accept that lying seriously injured in a field is not a good thing) but into the equation is how frequently does an accident like this happen?
I would argue so infrequently that it is almost irrelevant.
Having said all that I have no objection to booking out but as others have said there seems to be no longer a legal requirement to do so.