Why do some passengers get called to the desk before boarding their flight?

This happened to our party twice in our lifetime. The first time was when we were very young. It was regarding a pushchair that we’d checked into the oversized baggage. Apparently we’d left an item in the pushchair, but fortunately it could be placed into our hand luggage. The second time was when we’d already cleared passport control but the check-in hadn’t been processed properly so the clerk needed to see the passport again to complete the process. Sometimes the flight team need a little more information. Perhaps you need assistance to board the flight and the team need to make arrangements for a prompt departure. Sometimes you might be asked if you’re comfortable switching seats to accompany another couple’s request. Or perhaps you’ve bought too much duty-free and your boarding pass has been flagged. Someone might have a query about their destination. Or someone might be trying to reach you. There’s hundreds of variables here.