Never ask your users what they think before you ask your logs what they do.

Users lie. Users misremember. Users are inexpert at describing their own use of your software.

Logs don't lie. Logs don't misremember. Logs are experts at describing your users' use of your software.

If for some reason you didn't build your web app with an eye to getting useful information from your customers, start adding Google Analytics (or one of the numerous copy/paste Javascript competitors) and give it a few weeks to start collecting data.