Is thumbgen(or equivalent) necessary?

I was under the assumption that if all of your network stored media was in properly named folder/file format that the WD TV Live would automatically download the correct meta information, available fanart, etc.  I see an awful lot of talk on here about thumbgen and Mojo(not sure what Mojo is) and its making me wonder if I’m wrong.

Mojo is a theme:

No, Thumbgen is not necessary unless you are using a theme that requires Thumbgen to display the backdrops correctly for that theme.