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.

Edit: I don't think most people understand what I mean. I mean only the seed, so the 24th words are stored only online, and the 25th word never comes into contact with the Internet. The 25th word is also only typed on the ledger, and if it is long and complicated it would take forever to crack it. I have the seed stored offline, but I think about having a backup. My concern is if the seed gets lost in some way or other or get stolen, or another way to no longer have access to the seed. I've been thinking about that for a while now and I can't think of anything against it, because if someone has the seed they don't even know that there is a 25th word and especially which one. It would take forever to figure it out...