I wanted to chip in because i don't feel like enough emphasis has been put on the answer of this question...

If you'd extend your seed phrase with a long passphrase and share said seedphrase (minus the passphrase) online, you'd go from having a wallet that would require trillions and trillions of years using a whole server farm to hack to a wallet that could be bruteforced in a couple of years by somebody who has a couple GPU's laying around.
It's not just "not adviseable", it's really "not done"