Storing Seed Online

What is your opinion about storing your seed online and also using a long passphrase?

Theoretically this should be pretty secure if the 25th word is long and complicated. You would not enter the password anywhere online, only on the hardware wallet if the case should arise. You would also save the passphrase offline in a safe place, just in case. The advantage would be that you could access it from anywhere, since you would only have to remember the passphrase.

What speaks against it?

I am curious about your opinions.