Several websites advocate the benefits of Panels Everywhere (I have put them at the end of this question).
However, I have tried the module out out and cannot see the benefits.
A regular Panel page gives you the option to Disable Blocks. It also lets you display things like Menu Links, Footers and User Log-ins. So I'm not sure what Panels Everywhere brings.
I could never see the benefits of Panels, but Drupal Answers enlightened me and now I wouldn't dream of making a Druapl site without it, so I'm hoping it can shed some light on the benefits of Panels Everywhere).
Sites Advocating Panels Everywhere