Solid state drives (SSDs) are best used for operating system and application files where being able to read/write from/to those files makes your system perform significantly better than it would when using a traditional platter-based hard drive. You wouldn't see much benefit from putting files that don't change frequently (i.e. pictures/movies/music) on an SSD with the exception of videos/photos that you are in the middle of editing. Since SSDs typically are much smaller than traditional platter drives people tend to keep a platter drive available as well (either internally or externally) to store large media files.