Why is cloud save recommended for instant games?

Question

On the Instant Play Games site google recommends the following:

Integrate sign-in using Google Play Games Services and a cloud save solution to preserve progress in the game.

However in this other document the following is stated:

If the player is using a device that runs Android 8.0 (API level 26) or higher, and if your game specifies a targetSandboxVersion of 2, then the player's progress is transferred automatically to the full version of your game. Otherwise, you must transfer the data related to player progress manually. To do so, use one of the following APIs...

So it seems that cloud saves are not needed, there exists a simple API for transferring progress to the main app. So why is cloud save recommended? Am I missing some aspect or restriction of instant apps?

Answer 1

I found at least one reason for this, which seems critical enough: The instant app data does not persist over for example restarting the device. More info here.