Apps that are backed by some kind of service in the cloud should support multiple accounts. This is a no-brainer but several apps fail to provide this convenience feature. I’m particularly frustrated by the Kindle app. Though it could apply to other apps like Netflix.
Why would you need multiple accounts. Well, you might have a personal account and a business account, for starters. You may have an account you share with other family members, and so on. It is of course quite likely that limiting the number of simultaneous accounts to two or some such upper limit is desirable, for performance reasons and to prevent abuse.