In the point of safe keeping of our price key, seed phrase (mnemonics) is a very important thing to do, in other to avoid the threat of blossing/misplacing them. This is something that has to be kept in a place where only you as the owner has a full access to, so as you alone would be able to give account of anything that goes wrong. Using offline storage is said to be the best, which really is. There are lots of other methods used online, like wallets that provides the combination of hot and cold storage for the safe keeping of private key, seed phrase(mnemonics).
To me, the physical storage remains the best and safest amongst all.