This is true if you delete folders from your current driver revision. However, this folder keeps all previous ones as well. NVIDIA does not get rid of them automatically. It's safe to delete those old versions. If you look in my screenshot here you can see the two differently colored boxes I put around the groups of folders within installer2. The red box is from the latest installation (should not be deleted), the green box (safe to delete) is from a previous update that can be removed. You can tell the ones boxed in green are from a previous update due to the repeated naming scheme and the timestamp difference compared to the ones boxed in red.
So as I stated in my first post, the caveat for the CCleaner developers would be they would need to systematically determine what can be removed based on duplicate names. For example, you can see in the screenshot that there are duplicates of Display.Driver, HDAudio.Driver, and others just to name a few. The ones with the older timestamp are part of previous revisions and are essentially stale files that are no longer in use.