Is there any benefit to keeping resources in my clan castle?

Since clan castles generally have more hp than loot storage, they will be harder to be destroyed completely, and they will only receive loot once they have fully destroyed it.

According to this only 3% of the loot stored in your clan castle can be taken during a raid. Whereas 20% can be stolen from your gold storage and elixir storage according to the wiki.

Therefore it is safer to keep your loot in the clan castle if you don't plan on spending it immediately.

miva2 points out very good reasons, but also there's the practical side. It's a good idea to have your gold/elixir/dark elixir in whichever is guarded better (or closest to the center of your base). Additionally, goblins don't target your clan castle, because it's not classified as a storage. So, overall, I think it's better to keep your resources in your clan castle if you don't need them immediately.

There is another benefit aside from the one that miva2 mentions about the Clan Castle only being loot-able to 10% rather than the normal 20%.

This other benefit is that it can hold more resources than your current storage space allows. If you have max gold storage of 1,000,000 for example and currently have 900,000 and you win 200,000 then the clan castle allows you to store that extra 100,000 until you've spent the gold you have. Also you can only collect as much loot as you have room for in storage. So if in the previous example you collected from your clan castle 100,000 of those resources would go into your stores and the remaining 100,000 would stay in your clan castle