I think they are useful if you want to deal with people. For example, pretend you want to establish a business in a foreign country. Before you start you should probably know a little about that people's culture and society. What is the structure of their society, what do they value, and how does their culture shape their behavior? All of that is social science. Of course this is social science in an applied science.
Social science in a basic science sense becomes useless to a lot of people. Those who are totally invested in social science do it because they are fascinated with society and don't care about anything else. They will study things like how marriages differ across cultures and how society's separate themselves into different classes like castes or income level. They want to study how things like racism or conflict arise. They often engage in social work but they also study the subject simply because they like learning about culture and society in and of itself.
Sometimes I find society to be an interesting subject. Things that affect society tend to be more interesting then those that don't. However for most people this information is not that useful. It's definitely not useful if you want to build technology or something.
At some point we all deal with people so we all need to know some social science. but only some invest in it completely.
I also like to make a distinction between social science and social study. Psych, sociology, and anthropology are social sciences. The others I consider are social studies like geography, politics, economics, law, culture studies and the like. They're not trying to find underlying mechanisms, they embellishing on a particular or they're more applied in focus.
Anyway that's all my thoughts on the subject.