I find them most useful when there are many variables, or when I can see there's a relationship but I don't feel like trying out equation forms manually. It is

I find them most useful when there are many variables, or when I can see there's a relationship but I don't feel like trying out equation forms manually. It is indeed of limited use, since often I can spot the relationship visually. And once I get the general equation I can easily transform the data to get a linear regression.