When loading the texture, the pixel data is in main memory only. When using the texture in the actual rendering, this data has to be uploaded into graphics memory. This setting lets you decide if the copy in the main memory should stay there or if it should go away after uploading to the GPU. However, that part of the Javadocs is wrong for jPCT-AE (it's already fixed in the next version). The default for jPCT-AE is true, not false. And for normal usage, you want to leave it at that. If you set it to false, you have to deal with OpenGL context changes yourself and you don't want that in most cases.