Where are the Render files?

I just learned that every time I render a project a render file is created.

Where are they?  Can I look at them?

 

I see there is the option to delete them but before I do that I would like to know what they are.

 

Also, is there any reason to keep them?  Maybe I should just keep the last “rendition”?

If they are actual files they might be occupyig space unnecessarily.

 

Please advise.  Thxs.

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