You can't use any paid services as a starter account, although I did manage to get a free realm transfer to work. Those aren't offered very often though, and it was just to a South American realm, not a lot of use. I only tested it to see if I could.
You get a guild under your name. You can change the guild crest. You can type in guild chat. Those are the definite advantages. The guild bank is a possibility if you can ever get that to work. Apart from higher level enchants, there's also mats and various consumables that are easy to get with an 85 but a pain at 20. If you ever level the guild, there's also guild perks.