Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature you control may become lethal if The Walls of Ba Sing Se leave the battlefield during that turn
Incorporating equipment cards that grant evasion increases your chances of landing combat damage with this black commander
If you ran enough of them, it may even be able to change the tenor of the deck slightly, like running more Pact of Negation or other choices
Core Set 2020 previews are underway and your new promo packs are coming next week
Having the Azorius, Selesnya, and Rakdos Temples around should help those three color combinations right now, though, which should be especially interesting considering how strong all three guilds were last year and how all three seem to have taken a small step backward since then
It also helps keep them in check if they choose to go against the terms you lay out on who to target with your two copies of the spell