I know that some people, a lot of them probably, will wait until a raid can be soloed before farming transmog items from old content. That makes the feeling of seeing transmog runs (ToS, Argus, EN, Nighthold) not only fill up very quickly, but even have a surplus of people wanting to join!
How do you farm your coveted transmogrification pieces? Do you wait until you can solo or do you begin returning to the content of a previous expansion with groups as soon as you're able?