I'm done with a couple video projects and they left behind folders of rendered files that are many gb's and I need room on my laptop... Do I need to keep the .PRV folders???
Once you've finished a project, output your finished movie and you don't plan on editing it again, you can dispose of your preview files.
Worst case, if you do go back and re-edit your video, the program will just re-create them.
Just supplemental contribution...
If you delete the preview files in the Adobe Premiere Elements Preview Files Folder, the consequence is that you will need to Timeline render the associated Timeline files when you re-open the project involved if you really need a best possible preview view. The preview files will not be generated automatically in the re-opened project. The program will not just re-create them as is the case with conformed audio and video files.
If you delete the conformed audio files (Media Cache Files Folder), the corresponding Timeline files will regenerate automatically if and when the project decides it needs them.
Conformed video files are also automatically regenerated after deletion in the Media Cache Folder if the project decides it need them.
See Edit Menu/Preferences/Media.