async is a concurrency technique. If you need concurrency, async is required for node to work properly (not "better"). If you don't have concurrency, you don't need async. The point is you need to actually understand what async does for you and why. It's not inherently "better" for no reason and you don't need to memorize it as a "best practice". If the OP is writing a command line utility to alter a JSON file then exit, async complicates the code for no reason as the concurrency is not required.

async vs. sync depends exactly on what you are doing in what context. If this is in a network service, you need async. For a command line utility, sync is the appropriate paradigm in most simple cases, but just knee-jerk saying "async is better" is not correct. My snippet is based on the OP snippet for context.