Local dev beta findings
When using local dev (beta) your page will fail to compile if your LWC component has a nested folder containing helper js methods. The issue can be avoided by placing helper js methods in the root directory but I thought it was worth noting since having a nested folder structure with helper methods is allowed when developing and deploying. For example, I have a testComponent LWC which imports a helper js method which contains static json files from a nested "data" folder. The presence of testComponent/data/helper.js will result in the page containing the LWC to file to compile with an error:
500: Unexpected error fetching "/testComponent": An unexpected error occurred: "ENOENT%3A%20no%20such%20file%20or%20directory5Cforce-app%5Cmain%5Cdefault%5Clwc%testComponent%5Cdata%5ChelperMethod%27"
Similarly, if you have an LWC which only contains a .css file, a similar error will occur (requires the js file to be present). Again probably not a standard pattern, but it is functional and allowable by the platform normally.
