There are further advantages to the use of amp modellers for the gigging musician - even if you had the vast amount of vintage amplifiers that an amp modeller can simulate, you then couldn't get all that gear onto even the main stage at Glastonbury Festival. Even if you could, the sound engineer would probably end up having some kind of seizure trying to make it all work.
The use of the amp modeller (at time of writing, popular models are manufactured by Line6 and Behringer) makes life easier for the sound engineer, and provides musicians with the opportunity to create a hugely varied range of sounds. As well as the simulated amplifiers, these modellers also provide a large range of simulated effects pedals all of which can be output straight to a mixing desk and piped straight to the PA system, and routed to the appropriate onstage monitors.
Further advantages come from the lightweight nature and small footprint of these systems, as opposed to large, bulky and heavy amplifiers.