"it could be a way of seeing something of the event without having to get in place on a pavement first thing in the morning."
Though Trooping the Colour has no impact on London, apart from on traffic in the area immediately surrounding it, it's impossible to be within 100 yds of the processions or the parade ground without being surrounded by huge crowds. The gun salute from Hyde Park is a far-distant sound effect, utterly unconnected (except by radio signals to ensure synchronicity) with the main event.
Crowds elsewhere in London are no greater and no less during Trooping the Colour than on any other day of the year. The whole point of a real city in a benign climate zone and protected by the sea from physical invasion is that no one single event short of full-out aerial bombing raids has ever done more than scratch the surface of daily life since the Great Fire of 1666..