This free add-on allows you to replace a Region Render by an actual camera and places the render result back into the original frame.
It mostly addresses the issue that many network rendering tools and renderfarms don’t support region rendering. This add-on solves that problem for all of them and for most camera types.
Download it on Gitlab
Watch the tutorial
For the old farts there is a version for Blender 2.7x
The 2.7x version has the additional feature of splitting the frame in a grid to make distributed single-frame rendering, which has not yet been added to the 2.8 version for lack of a demand for such a feature. However, feel free to tell me if you would have a use for it.