On Telegram, login on a new device and you can see your all messages automatically. On Signal, you seems to need to perform it manually, and your history will lost forever if you phone are lost or broken.

I think the first kind of "backup" is what most people would expect, because it is convenient. But to provide this convenience, it can't be full E2E, so Telegram supports secret chat when you need max security if you are willing to sacrifice convenience.