Information on the Purge command is also available in THIS VIDEO.
The Purge command, (Tools > Purge) allows you to remove objects, classes, layers and resources within a specific document that are not being actively used.
When working with a Vectorworks document, any symbols, textures etc that you apply, then choose to not use later, will often still remain in your document, increasing its file size unnecessarily if you do not intend to use that resource again later.
For example, if you place a sphere within a new blank document, then apply a texture to it, that texture is added to the document as well as a resource, increases the document's size by 3-6MB. If you then change that objects texture three or four more times, you will have added three or four more textures, increasing the documents size by 12-18MB, even though you are only using one of those selected textures.
Using the Tools > Purge command, you can then select "Textures", you will see a number next to "Renderworks Textures" that lists the number of textures found in the document thatare not being used. Clicking OK will then give you a list of the textures to be purged, so that you have complete control over what is removed from your document.
Keep in mind that you may need to run the Purge command twice, since if your first purge attempt removed a class that had no objects in it, a second purge would then catch the texture that had been set as the default for that class, which is now not being used for anything after that class has been removed.
Edited by JimW