My understanding is that, just like the abstract algebra, category theory is a useful tool to help you recognize patterns and provide you some level of certaint

My understanding is that, just like the abstract algebra, category theory is a useful tool to help you recognize patterns and provide you some level of certainty about their behavior. Rather than figuring out yourself if you should do something one way or the other, you can say: Hey, I know it's X, and people smarter than me have proven that X will behave in a certain way and that I can do certain stuff with it. When building complex systems this can save you a lot of time and nerves. However, with a common, simpler software that most of us build, it's more about writing the eloquent and stylish code, than an absolute necessity for a programmer. You definitely can work in scala for years without knowing anything about it.