If you set QFE in an airliner, you will quite likely get the GPWS shouting "Terrain Pull-Up" at you. Although the position reference is from the FMS (usually derived from GPS these days), the altitude reference is barometric and if you set QFE the system thinks you are lower than you actually are. So if you 'adapt to local requirements' you will get the aforementioned aural warning. Had it happen once in Russia, (where the locals prefer you to fly on QFE), at an airfield with a 600ft elevation and in cloud!