CSS background-repeat tiles small pattern images seamlessly, while SVG patterns defined within defs elements offer resolution-independent scaling. CSS-only patterns using gradients and background-size can create geometric repeats without any image assets at all.
Custom patterns create a distinctive visual texture that becomes part of brand recognition — think of a signature geometric motif used across a site. Patterns reinforce brand identity more subtly than logos or colours, adding depth and character to otherwise flat surfaces.