It could well be distracting and inconsiderate to people around the user. Even worse is those who think they can record the performance, or relay to thei friends. Apart from being a sort of theft it entails obstructing the view of anyone behind and near the instrument being waved aloft.
I suppose these are the sort of people so desperately wedded to their "smart"-phones they dare not be without it. You see them even in supposed social situations with their friends, basically isolating themselves from the company; or letting the phones interrupt their conversations. Evidently they regard their phones as more important than the performance or their friends. They need learn normal social intercourse - and how to switch the gadget "Off".
They could be worse - talking through it, like the bunch of middle-aged chatterboxes in the centre of the stalls at a concert I attended.
The worst I saw with portable 'phones, thought not in a theatre, was a dozen young people in an outdoor-activities group, realxing in a club-house in the evening. The organiser was buried in her lap-top (probably work or study), a couple seemed to be watching a film on another; the remainder were all tap-tap-tap, scroll-scroll-scroll oblivious to their companions. This hermetic nonsense in Trappist silence carried on for at least the two hours before I left the building to seek real-world company in the pub.
About twenty or thirty years ago a British R&D organisation invented a form of wall shielding paint that would block or at least attenuate 'phone signals in rooms such as auditoria. I do not know if it was ever produced commercially.
......
Right, lunch-break over. I have real-world things to do... SW off, PC off, and go outside into the sunshine.
