In terms of the branch itself, sociology and its foundations are essential in education for a variety of reasons. When looking at how people learn, one must examine the sociological approach of the learner in order to understand how a student approaches learning, how the group to which the student belongs look at education, and how the narrative of the learner plays a dynamic role in the appropriation of knowledge taught at school. At the same time, examining the sociological foundations of a learner helps to expose biases and predispositions towards schooling. Teachers have to understand this because their students bring this capital with them into the classroom. To pretend that this does not exist and does not have a purpose inhibits the effectiveness of the teacher.
In your message to me you said that "sociological foundations" refers to the idea that education is meant not just for the individual's benefit but for that of society. It means that education should include instruction on how to get along as members of society. I will answer based on this:
I would say that sociological foundations are essential because modern society and modern jobs are much more interactive than they once were. Businesses, in the US, at least, often emphasize that they need students who will be able to work well in teams, often with people of different backgrounds than themselves.
In addition, many modern societies are becoming more diverse in terms of ethnic, religious and other sorts of demographic factors. Because of this it is important for schools to help children learn to deal with this new reality. It is hard for parents to do this because they are not as able to expose their children to others who are quite different from themselves. This is much more possible in school.
Finally, sociological foundations are important for societies that wish to be democratic. When students are expected to grow up to be participating members of a democratic society, it is important for them to learn democratic ideas and habits as they grow.
In these ways, it is essential for education to prepare students to be members of society rather than just teaching them information for their own personal edification.