Avoiding multiple levels of window management, when you want to edit multiple files and have one or more additional terminals available.
For instance, I've used this to edit a manpage with a live preview to the side in another window. Doing the same thing with screen would require running vim inside screen, and doing window management with both screen (for terminals) and vim (for everything else).
I like being able to have a vim window that has a terminal in it, there are some cases where I just prefer to have it in my terminal environment rather than switching to another real window. Mostly this is for things where I want to be in the same directory as my editor to run greps through my source, etc...
It's also nice sometimes to do something and then be able to search through the history with "/". At times I've then gone back and cut and pasted between the terminal output and a document I was working on, rather than using my window manager cut and paste.
I was, however, fairly surprised that I could no longer ":sh" out to run something. Had to get used to ":term" or ":spl term://bash".
Speaking practically, if you're using a terminal to use Neovim, you get consistent window management. If you're using one of Neovim's GUI clients, you also get a terminal in the GUI's frame.
For instance, I've used this to edit a manpage with a live preview to the side in another window. Doing the same thing with screen would require running vim inside screen, and doing window management with both screen (for terminals) and vim (for everything else).