Increased intake noise, which some think a benefit..
Reduced filtering possibly increased engine wear.
It might mess up the mass air sensor through over oiling the filter.
Generally speaking unless one is remapping the engine after other tuning modifications there are no benefits to changing the air intake filter. The OEM filter, properly maintained, is not a restriction to performance.
Any unauthorised modification may impact the warranty but unlikely to invalidate it.
Was the car bought with finance (PCP)? In which case the finance company would have need to authorise any modifications