Some people use it as an intermediary between lightning and on chain. For example, if you are stacking $50 at a time, it doesnt make sense to send directly to on chain in high fee environment and trusting a single custodial lightning entity to not rug you while you stack is more risky than trusting a federation of well known entities in the industry. When justifiable, the user can send their liquid to on chain in medium sized stacks nicely organized in a single utxo to their on chain. Nobody is reasonably cold storing on liquid, that is a strawman.

The second option is non custodial lightning, but honestly, it has a long way to go before the majority of people feel safe stacking on lightning before pushing to on chain. My critique is that we pretend that lightning is a viable option enough to put down liquid entirely.