Earlier this week, I flew LCY->EDI on BA. I was in 1B (bulkhead seat at the front, treated as exit row), and had a boarding pass stored electronically on my phone.
In LCY your boarding pass gets checked on entrance to the gate, and you put it under an electronic scanner. This either chirps and flashes green, in which case you get entrance, or it beeps and flashes red, in which case some form of manual processing is required. I've discovered often with an exit row seat you get a red flash, and they ask if you know it's an exit row seat and confirm you comply with the requirements, then wave you in.
On this instance, the BA staff member asked me to press the 'i' on the e-ticket, which turns it over, and scroll it down right to the bottom. The information on the bottom of the ticket is my BA frequent flyer type and number, the sequence number, and the e-ticket number. The frequent flyer type is on the front of the ticket too, and I cannot think why she would have wanted the frequent flyer number. She didn't look long enough to memorize the e-ticket number before she asked me the exit row questions, and then waved me in. I can thus only assume she was after the sequence number (020) which I believe just means I was the 20th person to check in on the flight.
Why would the gate staff be interested in the sequence number? If this is an interesting number, why would her own systems not have it displayed, as opposed to requiring me to do strange things with my phone?