A side issue is that non-trivial SVG authoring is painful to do by hand, so most people use some tool to do it. But the exported SVG will work on the rendering

A side issue is that non-trivial SVG authoring is painful to do by hand, so most people use some tool to do it. But the exported SVG will work on the rendering engine of the tool, not necessarily wherever it gets rendered downstream, and it can be difficult to know which features of your tool will result in rendering issues downstream. And sometimes the error is just missing content, others (like filters) often render the image completely black. It's like using a compiler that supports one version of an architecture and you need to learn what you can/can't do in the source code that will result in illegal instructions anywhere else. While Sketch is (imo) the best editor I've ever used for SVG it's also the worst about using weird SVG features that are poorly supported outside like, Safari and Chrome (I think they use the former).