How do you approach orientation in iOS and Android?

To anyone who has participated in the creation of a mobile app I have a question:

Was it designed/planned for both portrait and landscape?

If not: Why? Did you discuss this with your team? What was the rationale behind this decision?

If yes: Why? How much effort did you put into considering landscape scenarios for each screen? Did you design every screen for both orientations?

Context: I'm designing a mobile Bitcoin wallet on iOS (currently available on Android), and for Android this decision had already been made before I joined the team, but since I'm working on iOS from scratch, I want to answer and address this question with a solid logic. My opinion is that, even though landscape use represents less than 10% of the usage (source at the bottom), no app should determine how you hold your phone. With this principle in mind, I'm inclined to think that apps should be usable on both orientations.