Don’t use an overlay unless you have a clear, compelling case for why this content should not be presented within a regular page. Good reasons for using an overlay could include:
- The user is about to take an action that has serious consequences and is difficult to reverse.
- It’s essential to collect a small amount of information before letting users proceed to the next step in a process.
- The content in the overlay is urgent, and users are more likely to notice it in an overlay.
Kathryn Whitenton in https://www.nngroup.com/articles/overuse-of-overlays/