Why Cricut needs an SVG, not a PNG
A cutting machine follows lines, not pixels. When you upload a PNG, Design Space has to guess where the edges are, and it often adds a background rectangle or merges colours you wanted separate. An SVG already contains the exact outlines, one shape per colour, so the machine cuts exactly what you see.
SVG Harbor traces each colour separately into closed outlines, then stacks the layers so they overlap slightly. For layered vinyl that means no slivers of the base colour peeking through.
What about Silhouette and laser cutters?
The same file works. Silhouette Studio Designer Edition and up imports SVG directly, and most laser software (LightBurn, xTool Creative Space, Glowforge) reads it too. Use one colour per cut or engrave setting.