For players using physical cartridges or digital versions on a standard 3DS, the game is virtually unplayable in its raw launch state without this update. Version 1.4 introduced critical fixes that changed the way the game functions, specifically regarding the Battle Spot and online connectivity.
If using the Citra emulator, using a pre-patched Rev 14 ROM (without a separate upd file) is cleaner. If using a real 3DS, you want Pokemon Omega Ruby (USA).3ds (Base) plus the Pokemon Omega Ruby v1.4.cia (Update).
: This update is mandatory for accessing online features. Without it, you cannot use Wonder Trade , the Global Trade Station (GTS) , or participate in online battles and official tournaments.