Some people like to swap to story mode to grab leoric's crown really quick and then pop a ruby in it, though I think the usefulness of that is largely dependent on how mobile your character is.
You get one shot so don't cube something you can continue to wear without losing more than 10-15% of your damage. Cube it! Or if you find something else that's rolled poorly, cube it. Grabbing that weapon with the useful orange text is awesome for a few levels, then you need to upgrade to a real weapon. The challenge rift gives you everything you need to fully upgrade your smith (allows you to roll level 70 weapons with -level requirement) and allows you to cube a legendary. Just make sure you don't do the challenge rift of a new season until you make a seasonal character and log in to him first. You can use rifts to do most of it, the new challenge rifts make it a lot easier. Last updated at 14:00:17 UTC Weekly Help Desk RAGE Loot Thread Trade Thread