Having shell companies is a privileged situation for anyone perceptive enough to maintain one.
Your non-operating LLC is a good step in that direction. There are annual fees.
The primary advantage is that you can put the LLC's name on pretty much any asset or property or bank account or payment, and most people won't know it has anything to do with you. Some people might look it up, and if you want to further raise the bar of how few of those some people could ever figure it out, there are lots of things you can do with an LLC.
Finally, there are several tax statuses that the LLC can choose to have, some of which are permanent. As such, people don't want their personal body tied to a parallel tax code, but can easily spin up a new copy of their efforts via an LLC or other business entity type, where all the transactions to it are tied and taxed under that parallel tax regime.
Lots of other little perks. But you can direct anything through the LLC before you get to other your business idea.
If you aren't doing anything with it, why register it in Washington state? Use one of the states that offer more privacy, I know of at least 55 US semi-sovereign jurisdictions that offer LLCs, all with slightly different perks, mostly related to security, privacy, cost and speed. Big catalogue between every state, territory, district, even Navajo Nation has LLC statutes. Which one you want? Who knows. I like Wyoming.