Booking out may not have saved a single life, I bow to your superior knowledge. However it has saved valuable time in the ATS world and avoided much heartache on the part of ATS personnel! I doubt it keeps a single person anywhere in a job but it does make life simpler and safer for those who are involved in these matters.
I know the OP was asking about the legality of booking out. The thread has drifted! In the days when finding a telephone and getting through to ATS was more difficult I can almost understand the failure to book out. In these days of mobile telephones, it is a two minute job whilst walking out to the aircraft. Get real folks, stop being so selfish. Think about helping others for a change!
My days in ATC are way back and things may have changed but I do know that back then the pilots and operators who were polite, helpful and worked within the rules [like them or not] generally got the best service and were a pleasure to work with! The awkward uncooperative non-compliant personnel would often get the same service in return and it is very easy for ATC to give as they receive!!
H49