Glacier has a very clear use case, to my mind.

It is useful for keeping archives of massive data you're unlikely to ever need, but legally obliged to keep around, or just want to have available for a very improbable later examination. Think some huge transaction logs of two years back.

For a case like this, you don't need fast retrieval, and mostly you don't need retrieval at all. You plan ahead to only ever retrieve a small percent of these data. The rest will be silently discarded when retention period has expired.

If your use case is not like that, Glacier probably makes little sense for you.

This is totally not a backup which you likely keep in order to restore the entire state from as soon as possible.