We had some things that worked in our favor like the games being formatted in a square, so that worked really well to transfer them into mobile and make sure you can play the games both in landscape and in portrait.
Tommy Palm of King, via valleywag
Some mobile/tablet players have their devices mounted in a fixed position, such as on a wheelchair mount or bed frame, so are only able to play in a specific orientation. Others still have personal preferences, such as preferring portrait while playing one-handed on public transport, but landscape while on a couch at home.
Best practice example: Laddersnake