Safety in numbers and all that
Double-sleeving is where you put your cards in an inner sleeve before sliding them into the outer sleeve for an extra layer of protection against dirt, moisture and other hazards
As Ive said before, theres no quicker way to ensure you never get asked to play Commander with people again than by turning up with a deck filled with mass land destruction or not even mass land destruction, really, just any at all
Of course, there are some high-synergy cards that you probably want to make room for in your Urza deck: Etherium SculptorEtherium Sculptor and Foundry InspectorFoundry Inspector, Sai, Master ThopteristSai, Master Thopterist, Thought MonitorThought Monitor, the monocolor Urza, Lord High ArtificerUrza, Lord High Artificer, Urza's SagaUrza's Saga, and at least four artifact lands