Tiny aerodynamic gains from lack of cabling. But also allows more flexibility (sometimes literally, as anisotropic properties can be engineered into the layup) in the design of the composite material frames, as you don't need to worry about leaving room for smooth cable runs and the stress risers caused by holes/ports used to route them internally.
Wireless (and generally electronic) shifters are likely heavier on account of the battery. In theory they require less maintenance as they don’t have the breakage-prone cables. Shifts are quicker and require less force to activate, and also more precise because they don’t depend on the finicky adjustment screws. And they enable tricks like automatically shifting the front chainring to march your choice in the rear cassette (don’t pair the small front chainring with a small rear speed!), automatically choosing preset combinations, and so on.
Most racing bicycles are right up against the limit of the minimum weight allowed. Sometimes they even add ballast weights to stay over the limit, and fit them as low as possible as lower weight = better cornering performance due to moving the bike's center of gravity down/fore/aft.
