3D electromagnetic simulations are widely used during the antenna system designing phase, for both new products studies and for improving current solutions.
That approach has shown its high reliability during my industrial experiences and appears to be the best methodology for risk mitigation before the prototyping process.
ANTENNA SYSTEM DESIGN
RF CIRCUITRY DESIGN
RF hardware simulations are also often used during specific blocks designing phase, for both passive quadripoles (filters, dividers, couplers, impedance matching networks...) as well as active ones (Low Noise Amplifiers).
3D electromagnetics combined to RF circuitry simulation offers the advantage of SI (Signal Integrity) analysis and therefore prevent from any EMC issue.