Say you have a large model and you delete all but 2 moderately simple objects in it. Now you have a tiny model. You save the model and find that the file is still 30Mb on disk. When you open that file you find that it still contains all of the materials from the objects that were deleted. Is there anyway to purge materials that are no longer used to shrink the file’s size on disk? Thanks.
If you’re using SketchUp Pro, go to Model Info, and in the Statistics section, click on Purge unused. That will purge unused materials and components, and will result in a smaller file size.
Knowing that you are using SketchUp on Windows helps to answer the question you actually asked. You could purge only unused materials from the Details menu of the Materials panel, too. Sometimes that is preferable to purging all unused stuff.