When creating the wallet and backing up the account, you will usually be asked to input the seed phrase to be sure it is correct. That is the point where most people check that the seed phrase is correct but beyond this point, it is extremely important to check the seed phrase like once per year to be sure everything is fine. It will be so painful to continue sending Bitcoin to a wallet without a backup or whose seed phrase have been lost.
Most wallets no longer ask you to write down every 12 words from your seed phrase, the verification is passed by identifying a few words at random based on how they are serialized, wallets don't stress using every seed phrase to verify the process.
Seed phrases are words, 12 words that can all be memorized, i don't know how a person cannot pen them down without error. After writing, what is next is to cross-check if there was any mistake, you don't need to check or keep checking once every year, seed phrases don't change.