Some people seem to use them as a database of common programming patterns, but that's something I already have, both hundreds of scaffolds in many programming languages I've made myself and hundreds of FOSS and non-FOSS git repos I've collected out of interest or necessity. Often I also just go look at some public remote repo if I'm reading up on some topic in preparation for an implementation or experiment, mainly because when I ask an LLM the code usually has defects and incoherences and when I look at something that is already in production somewhere it's working and sits in a context I can learn from as well.
But hey, I rarely even use IDE autocomplete for browsing library methods and the like, in part because I've either read the relevant library code or picked a library with good documentation since that tells a lot more about intended use patterns and pitfalls.