Originally I though this might be a good way to improve FPS by having the UI still crisp but the 3d world in a lower resolution. However, upon examining it a bit more it seems its actually just rendering a camera to a separate render target image.
My question is: Would this help in any way to improve FPS? It look to me like having a render texture would actually just slow things down. Am I right?
If you are looking for ways to increase performance and you are having device pixel ratio turned on, you can tweak or let the user choose what the ideal setting is.
Some devices have especially high pixel ratios, in the range of 2-3. You can easily tweak it using this property: