"If they're performing a task quickly because it's easy, or slowly because they're struggling with the UX. And you find out that customers on a certain mobile device are suffering huge performance issues, for example."

...

"You don't know these things until you measure them."

If you don't build big, bloated tools using ultra-high-level frameworks and if your product is a simple tool that performs a single, useful task ... then you do know these things and you don't need analytics to tell you.