Links created using the New button in either the PoliteMail Builder or content data grid are called User Links.
Links set up through the Insert Hyperlink feature in a New Message are saved links.
Links set up through the Insert Hyperlink feature in a New Message are not User Links, but they will be still be counted in the click metrics. For example, a user adds an image and then hyperlinks that image to a video on YouTube. PoliteMail metrics will count how many clicks this image received, but the link will not be available in the PoliteMail Builder or in the links drop-down menu. You would need to create the link with the PoliteMail Builder or data grid.
Adding a user link or a saved link has no bearing on measuring that link. PoliteMail measures ALL links in the email, even those embedded in email signatures. The key difference is format and sharing. User links can be shared and will appear in the PoliteMail Builder, data grid, and message as the name you have assigned to them.