In all airports, it is a requirement for passengers to have their boarding card checked at an automatic gate before processing to security which can also determine if the passengers have gone through security by having their boarding card checked.
Also I know some airports like Heathrow that you have to go through security 35mins before departure, at the boarding card security check, would it be possible to refuse access to someone who is there less than a specified time before departure as realistically if they were allowed through security they would still essentially miss their flight and the passenger loading would be based on who’s gone through security in contrast to who has checked in as passengers on landside would have no way of making their flight.
Well, not all airports. For example I was in Australia a couple of times, the last time a half of year ago, and the boarding passes were checked only once, at the last step before departure, i.e. at the boarding gate. At domestic terminals no boarding pass or passport were checked before passing the security - it was all the same in Adelaide, Melbourne or Brisbane, and at international terminal the passport was scanned instead of the boarding pass, and then the boarding pass checked only at the gate. In European airports on the other hand, yes, I’ve had boarding pass scanned before security. There seems to be no pre-ticket check in Australia, however at international terminals the ticked is likely checked with the passport scan.