Well it's the only way for the monerujo side of garnet to connect note IDs with transactions, it's not really a problem but there have been problems where a wallet has trouble syncing subaddresses that are really far ahead and it doesn't look far enough to see them. So you import your seed elsewhere, a transaction doesn't show and you have to manually set it to look further ahead for it.
Discussion
I see I didn't know this a thing
was a thing*
Yeah so subaddresses function like the wallets in BIP39 seeds, where they're deterministically generated from a seed key and that seed key is your private key. For a wallet to know about a transaction sent to one it has to know it, and usually wallets will auto generate a bunch of them and check, but if you've created thousands of them then it won't know to look that far ahead and you have to tell it to.