Always happy to engage with visitors when we are at exhibitions. I cant imagine exhibiting and then ignoring those who have taken the time to look at your layout.
Loads of examples.
Answering questions about a piece of rolling stock, explaining how something was built, explaining how say flexi track is used or wires are soldered to track etc etc
Accommodating a request to see a particular train they have seen in the fiddle yard, or slowing one down to allow a train to be photographed at a particular point on the layout.
Last year we were exhibiting at an event with a layout in mid 80s guise.. At one point there was only a few visitors, I heard a boy talking to his dad, they look like Mk2 coaches he said, impressive I thought (better than half my club), then later on I heard him trying to decide if the coaches passing him were Mk2 d, e or f, very impressive (better than most of my Mk1 maroon liveried loving fellow club members!). So we had a wee blether about the differences in Mk2 coaches, then when things quietened down a bit more, we invited him in to help operate, he had a ball and stayed for hours. He and his dad now come to our club on a regular basis travelling the best part of a hour.
Yes as per the OP sometimes things go wrong and the focus has to be getting the trains running, but even then it is unlikely all the layout operators will or can be engaged in dealing with the issue. Quite often the less technical amongst us find we have a wee bit free time for a blether with the visitors who are wondering why not much is happening at that precise moment.
One of our previous layouts, Barnhill Camp had the control panel and stool for the yard area out the front amongst the visitors while the panel for the twin loops was located in the "normal" location inside the layout. The yard area was based on a yard where WW2 tanks etc. were being loaded onto trains in preparation for D Day. The layout was built to display a former members interest and by default he used to sit out front, he was best placed to explain every train and piece of military hardware featured on the layout.