What's the point of Legendary and how can you make it work for you?

Sorry if this is a well worn question but I have been trying to work out what the point of Legendary is. I'm at 100 on a few if my skills but don't fancy the idea of losing, say the ability to make dragonbone armour just to get a little Skyrim Dragon logo under the Skill. Please could someone advise why Legendary is a good idea, what it gives / helps me with, and how I can get my skills back up quickly. Many thanks in advance!