Requirement for a golden simulator

Hi folks,
I would like to ask your help to give an answer to a very basic question:

what are the main requirement an EM simulator must satisfy to be
a profitable, daily usable simulator?

What are the most valuable characteristic for an EM simulator?
Is it the user interface or the accuaracy .....or what?

Thanks in advance to everyone

SecondaLinea

wellcome to Elektroda Giancarlo

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