Opening lockeds is a very bad idea. Don't believe people that tell you they looted an arcane shard and the solution to world hunger from the first crate. In my opinion, spending plat on something that is permanent is the best way to go. Here are two of my favorites:

- The Jumpstart Bundle! - Located in the 'Shop.' I buy one of these for each of my alts. For just 40 platinum, you get 50 inventory slots, 10 auction slots, 25k gold and 200 potions. If you were to buy the inventory and the auction slots individually, they would cost 105 platinum for the same amount! After that you should stick to using story tokens for additional inventory and auction slots.

- If you're after achievement points and titles, there are some necessary pets that can only be purchased with platinum.

On occasion, items purchased with plat sell for four or more times STS's official 1 plat to 1000 gold exchange rate. For example, if an energy kit is selling for 20k (you buy for 5 plat each), you will get 4k gold for each plat. It's up to you whether or not you want to cash in at that point.

I hope this helps!