Use of large PictureFill symbols in ArcScene will result in large scene documents (*.sxd).
By design, PictureFill symbols are saved with the document; thus, if large images (example, used for globe image texture or detailed trees) are used for feature symbols, they will create large documents on disk.
Avoid using large images as a source of PictureFill symbols. Most systems will resample large image textures to 1024x1024, so there's no point in using a source image larger than this. Resample source images ahead of time.