Realmling hit the nail on the head.  I have a separate runtime for stuff that I work on from scratch.  Also have a special runtime for projects, those thoughful scenes that require special content for one time use only.  Afterwards, the content of the folder is either deleted or transferred to disk for future consideration.  What is important, keep your frequently used content together for easy access.  Use what is necessary for your project and then delete afterwards.  Always keep your purchased/freebie content in a safe place (disk, external HD, etc); don't unzip and delete them.  Usually the readme's will have specific instructions or special free offers.  You will be surprized how quickly your library will grow.