Do you know what you're doing when you yell BRAVI!! a split second into the final chord?
Especially if there are microphones above the platform?
The orchestra may be recording the piece. If you yell BRAVI - or indeed anything else - before the sound has quite disappeared, you are disrupting the recording.
The entire orchestra will then be kept another half an hour in the hall for a quick patching session.
These days most members of London orchestras, especially the younger ones with families, can't afford to live in London, so they have very long journeys home to places like Tonbridge, St Albans, Lewes or Bedfordshire - when they'd rather be in the other kind of Bedfordshire a little sooner. And with petrol prices high and the congestion charge/parking fees making a car in the capital basically pointless, people take trains.
Our railways, however, still function on the presumptions of c1958 that nobody is out after 11pm, that nobody has to go on tour early in the morning, let alone on Sundays, and that there are only a handful of people in London anyway, so trains late in the evening are few and far between.
When you yell before the music is over, and it is not over until that chord has died away, you ensure that more than half those musicians will miss their trains home. They will in many cases have to wait up to another hour for the next one and will get in at some unearthly wee time of morning, completely knackered.
Their spouses will be knackered too, will be fed up with the schedule and may spark a fight. Their children may wake up at the sound of the front door. Everyone has a bad day in the morning, whether at school or at work or on tour. An exam may be shakier than it should have been due to exhaustion. Someone at work may make a mistake in some words or figures or diagnosis. Someone may be late for a vital meeting. And so forth. Everyone does their best, but would have done better still with an extra hour's sleep.
The recording, meanwhile, may be entirely jeopardised. And it doesn't cost nothing to set it up.
This is all because one person in the concert hall couldn't hang on just one second to yell BRAVI.
So please, please, please: THINK before you YELL.