It's previews. Period. I found that even when he was asking for opinions, he really wasn't open to them in the slightest. Not worth the $2 in my opinion.
If you are asking to tell a artist what to do, that is called a commission. Those usually run higher than a couple of dollars.
$2 is a subscription for already commissioned art. Considering many of us have payed $50 or more for a art book, it's not a bad price.
Not a Patron myself, need to save money where I can but it's one of the more tempting Patron offers.