This is a great question. It is best to start with a definition of sociolinguistics. Generally speaking, sociolinguistics is the study of how language is shaped by society and how language shapes society. There are many insights that the study of sociolinguists can offer.
First, the study of sociolinguistics can offer insights on the use of language based on class. In view of this, sociolinguistics can ask interesting questions like, does the use of language play a role in social mobility?
Second, sociolinguistics can also study things like the use of slang and how slang can become mainstream.
Third, sociolinguistic can also study the variations of the use of language based on groups in society. It can come to insightful conclusions like how the use of language can reinforce social norms and how the use of language shows who is and is not part of a group.