I am currently helping to create a website that uses .less and css at the same time. It is simple enough and you can get almost everything working. But I hit some major brickwalls while doing so. For example I couldn’t find a suitable way to solve the issue that a child theme won’t work (I am sure my ignorance is a big part of the problem).
The other was that the theme I am working with wasn’t built with maintainability in mind, I really would have loved some un-minified JS files, some structure in the CSS and finally more helpful comments here and there.
I slowly start to get why my mentors were so annoying when it came to coding hygiene and coding standard - I hereby promise to do better when it comes to all these topics - only after I suffered from the consequences when you are not.