Yes, that was one of the concerns. I am happy to hear that the transfer limit does not apply to cross-canister calls. Thank you for clarifying.
Probably better if someone from DFINITY confirms this.
The other reason is to wrap objects into a generic format for on-chain backup of one or more dapp canisters.
I think there’s an upcoming feature to let developers download the state of their canister to somewhere offline and off-chain. For this exact use case of protecting against data loss during canister upgrades.