TidBITS:

For those struggling to free up space, particularly on a notebook Mac with relatively little internal flash storage, Optimized Storage sounded great, at least if you don’t mind paying for online storage in iCloud Drive. And while it could be a great boon for such people, it turns out to be a somewhat confusing collection of seemingly unrelated features, burdened by one of the stranger interfaces that Apple has produced in recent years.

Plus, although we haven’t had time to test all the possibilities, I recommend care when it comes to Optimized Storage in general, and extreme caution with one of its settings. That isn’t to say you shouldn’t enable all its features, but that you should understand the possible implications before doing so.

“Optimized Storage” sounds like another one of those things that would be great – in theory. But, in practice, I’d be very careful about using it.