What has been the initial motivation for this procedure? Just gathering the data and rejecting people not willing to give in or actually looking for red flags j

What has been the initial motivation for this procedure? Just gathering the data and rejecting people not willing to give in or actually looking for red flags justifying the denial of entry? If the latter applies, what does the set of red flags look like? I assume the given example in the article is not part of the initial motivation but rather consequence of misbehaviour of the guard.