Most characters have a profession—doctor, cop, assistant in a cupcake store—and in the course of doing their job they will slip into work mode. They will talk and act in the way you expect someone in that position to talk and act. The problem is that this can make them come across as stereotypical.
This is especially true for secondary characters who might not appear often other than to perform a job related task, but it can also be true for main characters where every time they have to do their job they start acting in a very specific manner—a politician uses a lot of meaningless double-speak, a doctor uses a lot of medical jargon, a cop becomes focused on factual questions and answers.
This makes it clear what they do for a living but little else.
What a character says and how they say it not only tells the reader what kind of a person they’re reading about, but also helps to set mood and tone for a scene. There’s a lot you can do through dialogue beyond asking and answering questions and imparting information.