I currently have all my media stored in folders within a media dataset. The UI reports how much space the media occupies, but I don't get any immediate feedback into how much space different types of media are occupying. So, yes, I think it's a good idea to place different types of media into their own dataset. Doing so, you will get more reporting information from the UI and a better insight into the types of media you own. It would still be a good idea to group these datasets together, by setting up them up as child datasets under a root. eg. media dataset with child datasets movies, music, pictures, video, etc. This way, the UI still informs you of the total space all media occupies.
The other advantage of separating different types media into their own datasets is that an application may only be concerned with one type of media eg. for something like Plex, all media datasets are mount point candidates, but for a music player plugin, only the music dataset would be applicable. You get this type of granularity using separate datasets for media type over a single media dataset.
Note: What's stopping me from doing what I suggest and not what I actually do is that I'm too far down the track to change things. For instance, if I did, Plex would refresh all its metadata and I would have have to go in and manually tidy things up. With a substantial library, this is not a trivial task.