The most important uses in mind are that you can use Bitcoin to hedge against your own currency and as a way to diversify your portfolio in the same way you might hold stocks, bonds, cash and gold.
You can definitely argue that people shouldn't keep all their wealth stashed as dollar bills under their mattress, and that they should diversify.
Indeed, absolutely nobody advocates doing that. Everyone says to diversify, except for goldbugs and bitcoin extremists.
The question of whether it would be a good idea diversifying in that direction is still unanswered, as there's plenty of real productive assets to invest in that contribute tangible goods and services to the world.
When people are in a frenzy bidding up the prices of things that aren't providing goods and services to anyone, then you should worry.
While in theory it is probable that btc growth will never be as astronomic as it has been in the past, you can't time the market, and there's no telling where the true ceiling is because this market is so inneficient.
Aside: the inneficiency I think comes from ignorance and manipulation of btc, not a flaw in btc itself.
Worth considering, especially now that there are better alternative blockchains.