SVG is rendered (rasterized) by the browser. The browser can then cache the rendered image to avoid wasting CPU cycles.

SVG often includes raster images? That's very surprising to me. I can see some use cases here and there, sure, but using a vector format to 'often' include raster images... i dunno.

Thousands of XML elements is the ideal case, compresses extremely well.

An example, many of Inkscape's filters depend on raster samples that need to be embedded. Complex gradients are also rasterised.

SVG can be rasterized into a cache and just blitted or composited as necessary.

No point to waste CPU cycles rasterizing same SVG image repeatedly.

One would assume the browser already renders the svgs once and the caches it. Maybe, who knows, probably depends on the browser.