RGB fixtures mix red, green and blue to produce millions of colours, and for saturated colour washes they are perfect.
Where RGB struggles is white. Mixing R, G and B to make 'white' gives a slightly off, low-output result that never looks as clean as a dedicated white LED. That is where RGBW comes in — a fourth white channel that lifts brightness and lets you hit true whites and clean pastels.
Use RGB where the job is colour: facades, bridges and fountains that live in saturated hues. Reach for RGBW where you also need crisp architectural white — hotels, monuments and premium facades that alternate between colour shows and elegant white light.