This utility is unbelievably useful. Modern ide's are quite good at finding redundant libraries or variables but sometimes the front end misses out.
One problem that may take a bit of manual work with the result is the use of heavy bundling. It could be a handful to split the results into the correct css files for organisation.
There's no arguing that years of maintaining, adding, and removing from a site will add excess code to the codebase. That excess code comes at the cost of users who have load the extra code, so eliminating the dead code is important.