Sure that work is going to happen but often what you see is multiple stylesheets loaded using the async hack which results in multiple style and layout calculations as the browser can coalesce them because it doesn’t know that they’re stylesheets or when they will arrive
The whole philosophy of critical styles philosophy being those about the fold is a mistake in my view
Far better to adopt approaches like those recommended by Andy Bell that dramatically reduces stylesheet size
And do critical styles “correctly” i.e. load those that are needed to render the initial page and load the ones that rely on interactions separately
There are definitely better ways, however, for some scenarios and time constraint, this tool was really useful, e.g., I used a template, since the budget was tight and it had 10,000 of lines of CSS and I had to do something quickly to improve UX and Lighthouse results, the template had bootstrap, revolution, etc.
The whole philosophy of critical styles philosophy being those about the fold is a mistake in my view
Far better to adopt approaches like those recommended by Andy Bell that dramatically reduces stylesheet size
And do critical styles “correctly” i.e. load those that are needed to render the initial page and load the ones that rely on interactions separately