First two A320 operators had this SOP, last 2 haven't. On some older MSNs with FMGC v1, after landing the box crashes dumping whatever you had stored (waypoints, routes, secondary). Some believe switching off the FDs prevents this (less demand on the processors?). Switching off the FDs then progressed into switching off all lights on the EFIS panel and that's where we are today. It should not be an SOP anywhere IMHO.