One of my friends said he understands that If you give away your private keys to someone, they can basically be used to drain your wallet of all its holdings. Which makes private keys so much so private and should always be stored securely and never shared. But something is not so clear about this keys as in the statement below:

"for Non-custodial wallets, it is required you to store your private keys, as it gives you sole responsibility over sensitive data."

First, are private keys for Non-custodial wallets to be looked out for and stored/saved just like the seed phrases? And

Secondly, what other times would a wallet owner need to personally use the private keys aside from its primary automated role of authorize transactions?