How well does this technique work for goals where the path isn't so clearly defined? Say you want to "launch a profitable side business in 2021", how would you fit this into that? You could have a daily goal of "work 1 hour a day on my side business", but that could easily end up with you spending 365 hours reading blogs on starting a side business and not getting anywhere.
Beeminder encourages you to define and refine your metric to make sure it doesn't fall prey to Goodhart's Law. Of course it's your own goal and so it's much less susceptible to Goodhart's Law. You actually care about the underlying goal!