Performance impact when CU_EVENT_DISABLE_TIMING isn't specified

CUDA API doc says that if CU_EVENT_DISABLE_TIMING is NOT specified in the flags when calling cuEventCreate(), it affect the performance of cuStreamWaitEvent().

[CUDA Driver API :: CUDA Toolkit Documentation]( CUDA Driver API :: CUDA Toolkit Documentation )

But actually, under what specific conditions and in what way does this impact occur ?

How about in the case of cuEventSynchronize() ?