It provides great insights to understand what is wrong with our APIs, which in turn helps us fix things faster than doing manual testing would have done! I like that we can easily track changes within one or more components of each service at once as well (using versions).
Nothing so far really - though they did recently change their pricing structure & features from freemium model where you could use it without paying any money but was limited by only 10 calls per day etc., into paid plan now