There is another good reason on why ATC should tell the aircraft to hold at the CLP if needed. ATC should be ready to give Expected Approach Time at the same time so that crews know what to plan for based on fuel remaining. Even if crews do the right thing as you expect and enter the hold "automatically" , expect frequency clutter when they start asking about their EAT time. It is more efficient if you just tell them to hold, including EAT time.