What does "We improved your import" mean?

A plan you analyzed but did not approve can be looked at by the Podspun team. When they fix something in it (a page that came across wrong, a theme, a missing channel), they leave a note on the plan and email you. The note appears at the top of the plan on Imports Ready and as a To-do on your Dashboard.

Open the plan, click Preview draft of website to see the draft site as it stands now, then Approve and start migration when it looks right. Nothing is charged until you turn the site on.