Sprints Taskboard vs. Boards. How do you use Azure DevOps Boards?

Hey everyone, I'm building a tool to integrate with AzureDevops boards, and in my study of the platform, I realized that there are two ways to use boards. The first is in Boards, and the other is in Sprints Taskboard.

So I'm wondering, how do you control your tasks? For example, which board is most commonly used to get info to track software engineering metrics (lead time, throughput)?