Once the DNS records have been changed to point to a transferred site, we have to wait around without any feedback and hope that the Auto Let's Encrypt system sees the DNS change and then installs the cert for the domain.
When your new site is sitting there and people who access it are getting a "not safe" error message, you want to know that the cert will be installed asap.
We should be able to click a button to tell the system to check DNS and install the cert.