Why can’t we just use the PA and turn the reverb knob to “wet” ?

Magne Skålevik_400x400

Or, creating virtual performance spaces with electroacoustic systems

Magne Skålevik, Brekke & Strand AS

Can a small, dry room be transformed to a bigger, more live one, by just pressing a button? Why not just use the PA and turn the reverb knob to “wet” ?
Since starting out as scientific experiments in the 1950s, electroacoustic reverb systems have developed into the numerous applications utilized today. Some are used to simply add reverb to the amplified (PA) sound, some (more advanced) to enhance or add the little extra to single purpose performance space (theatre, opera, classical music), while the most sophisticated systems are meant to fulfil the old dream of the ultimate versatile space that covers every demand in the span from dry cinema to symphonies and choral works.

However, it is important to be aware of constraints:  Regardless of your choice of technology, you have to play along with the room somehow, direct sound from the music instruments should not be masked, and - not every room can be used for classical piano, string quartet or symphony orchestra.
How should the sound engineer relate to and use such systems. Are there benefits of other program settings than "dry/off"? Are there any side effects of changing the parameters of an electroacoustic reverb system during performance?

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