Can I clean up Premiere Pro CS6 preview files like this? I did a test with a small Premiere Pro CS6 project and discovered that for each change I made to an effect Premiere generated a completely new preview file and stored that alongside the old file ( which was apparently trash at this point ) 

Eg I did a rotation change and rendered a section and it created a preview file. I repeated this process and it made a second file. I would have expected it to overwrite the original because when I deleted all the preview files and generated a new preview it only ended up with a single preview file ( seemingly the same file as the last created ) — so I'm concluding that it would never use the previous 4 files yet it didn't delete them or give me an option to.

The reason I did this is that the preview files folder in my main project is 15GB in size; and I'm assuming much of this is trash based on the above. So I moved it out of the project folder pending deletion and generated a new set of preview files for the project, which which came out around 8Gb - and it seems to work fine.

My questions is:

Is there any problem with this method of regaining space other than it takes time to regenerated the preview. I mainly am curious because I haven't seen a reference to this technique anywhere; and also because I wonder why Adobe didn't add a button to purge and regenerate preview files (at least that I've seen) since it's fairly straightforward and reclaims back so much space.
You can delete Render files by going:
Sequence > Delete Render Files

Or by using third-party programs.