Questions on Background rendering

Hello All-

I'm using FCPX with rendering turned off, I plan to render when I need to, seems most people are using the application this way. I did a search but wasn't able to find my questions. That is: #1) Do you have to render everything before exporting your film?

For example, if you re-timed a clip you have the choice of "Video Quality"--->Normal/Frame Blending/Optical Flo for smoother transitions. I assume if you wanted Optical Flo you have to render it, and best do it at the moment, for fear you forget. Being new with the App I can see I may not catch all of what should be rendered before export if I leave Rendering off in Pref's.

So, would it be correct to assume at least for safety sake, you should render all before exporting your film?
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Question #2) If I wanted to delete unused render files is that possible?

If I select a project and go to ---> File, I only have a choice to "Delete Generated Project Files" nothing elsewhere that I see stating "renders". Similarly, if I select a Library, and go to ---> File I only have a choice to "Delete Generated Library Files". Are "generated Files" actually the rendered files, & if so, is there a choice to delete unused/used render files?

Thanks for any information,
Robes

1. No.

2. When you select delete generated files you have options on which files to delete.