Mirrorless technology paved the way for the face detection and eye detection autofocus systems that we know and love in modern cameras. This is because older DSLRs relied heavily on the best autofocus being achievable when the mirror was down, as the faster AF sensors tended to be up top in the pentaprism housing.
Switching over to live view would often be a painfully slow and inaccurate affair on many of the DSLRs I owned. But with the removal of the mirrorbox and optical viewfinder, we saw mirrorless cameras that had no option but to autofocus using the on-sensor data.
