I thought that it would be nice for this option to automatically get disabled if "viewport selection" is used and nothing is selected, instead of displaying an error message. This would allow a workflow where you select some object, tune it's parameters (only the viewport selection is rendered then), then you deselect all and you are free to navigate the scene using IR, and then you can select some object again, ...
Would be super cool with fully working "clear vfb inbetween renders" off.
Didn't want to submit it straight to Mantis as maybe some of you will see some drawbacks of this and would like to discuss stuff.