If I store my 12 words recovery phrases for the wallet (in paper), why should I choose a more complicated procedure storing 27 words in order to get paper wallet certificate?
they both al least have the same function, or not? what I am missing?
Daedalus 12-word phrase is a backup for recovering in Daedalus, if you write those words down on paper and keep them very-very safe you are good. The other option is to have a paper only certificate, you will not see this certificate, once created in Daedalus, nor can you send ADA out if you have a paper certificate.
You are not missing anything, just pick which one is right for you, or do both to see which one works for you.
Do add a strong spending password in Daedalus, this password encrypts your keys, you really need to keep them safe, so set a strong password in Daedalus. One more thing, if you ever forget or if you ever restore your Daedalus from those 12-words you do not need to remember that password you set, the password is not saved to the blockchain only your computer.
You could do that, but a paper certificate also allows you to transfer to it, I have a couple of paper certificates that I add ADA to them whenever I can.
PS nice breakdown, you could also generate multiple receive address for more privacy, before uninstalling Daedalus.