Also, as your storage hits 97%+, you'll probably start seeing effects in your business metrics, and then you can look into it.
real-time, high precision metrics aren't necessary. when you say that you don't need metrics and then say that you can poll metrics periodically, you are contradicting yourself.
Unless you want to be able to have trends over time, either for capacity planning (needing to order more storage in case of bare metal, or planning costs ahead) or to correlate with other things (storage consumption is growing twice as fast since deployment X, did we change something there?).
You don't need to have 1s granularity metrics on storage consumption, but having none is just stupid levels of fake "optimisation" that will cost you more in the long run.