I noticed I have 30gb or more of folders in a folder called preview files. These seem to be the product of rendering and look like a waste of space - what happens if i delete the whole lot for projects i no longer work on? would removing these and the CFA and PEAK files damage the ability to work on the file at a later stage? I could use the extra space!
First of all, there is a difference between preview files and Media Cache files.
Preview files are those, which are created when you render the timeline. By default they are .mpeg and .xmp. If you delete them via Sequence -> Delete Render Files, .mpeg files, which represent the current state of your timeline, will be deleted, whereas the rest .mpeg files, which represent older state of your timeline, and all .xmp ones remain.
If you delete them manually, i.e. without going to Sequence -> Delete Render Files, you will be asked about some missing media on that project re-launch.
Media Cache files, some of which are .pek and .cfa, are created when you import assets into a project. You can check the Media Cache files location via Preferences -> Media.
Deleting all files from both Media Cache and Media Cache Files folders is safe: PrPro will rebuild Media Cache Database from scratch on restart. Moreover, deleting all files from both Media Cache and Media Cache Files manually sometimes helps fixing Dynamic Link or Importer Generic Error issues.
As Jim says, yes.
In fact, I keep my cache and preview files on a separate drive, making it easy to delete them all at one time and then defrag the drive with nothing to speak of on it. Much faster and keeps my editing speedy.