Couple crypto cold wallet questions

I finally stopped being lazy and got myself a cold wallet, specifically the Trezor Model one. Setup was extremely painless and simple. On day 1 I did a test transfer from coinbase to make sure I had it down right, then on day 2 I transferred the rest of my coinbase holdings onto the trezor. NO issues. 2 questions though:

1) It's been hammered home repeatedly how important the 24 word seed phrase is. Taht was part of the setup process, but on day 2 it wasn't used in any way. During setup you can choose to set an *optional* PIN, which I did. So on day 2 I had to enter my 4 digit pin right when I connected the trezor to my computer but that was all, when I did the transfer nothing seed phrase related was needed. I guess i misunderstood it's purpose...is it only used in a lost/stolen kind of situation? I assumed that you'd need parts of the seed phrase for any transactions.

2) I had to download the Trezor suite onto my laptop to help facilitate the transfers. Have y'all ever sold directly via that platform? It occurred to me that Coinbase knows all my bank info and personal information, but the only thing Trezor knows about me is my name and email. So at the moment if I wanted to do a big selloff I'd have to transfer to coinbase, wait 30 minutes til it finalized, then sell. And honestly I don't mind doing that, just curious if any of you had experience selling directly from teh platform with your wallet connected to it.