When to use it
Use it when you're asked something you can't answer on the spot, especially by a manager or client. Saying you'll find out, with a specific time, turns a gap into a commitment. Then follow up by that time, even if the answer is still partial.
Example
Client: “What's the turnaround on custom orders?”
You: “Good question. I'll find out and get back to you by 3.”
Client: “Perfect.”
In an email or Slack message
In Slack: “I don't have that number yet. I'll check with ops and reply here by 3.” Then reply in the same thread so the answer is easy to find.