It’s confusing when some apps show in landscape and some in portrait. Even different screens within each app. For example, FaceTime supports landscape for the actual call, but not for the contact list. Because of this inconsistency  , I never know what orientation the device is in, and whether the rotation lock is on.
Make it uniform. Both Android and iOS should require all apps, and every screen within each app, to support both orientations, for a consistent and frankly sane user experience.
 As if this is not bad enough, some apps like Instapaper have their own orientation lock. Grr.