The only benefit of Pattern, in my humble opinion, is the extra $15 per month that Etsy will make from you.
You get nothing in return. It is NOT a standalone website.
It is just kind of a copy of your shop, with the illusion of a standalone website. You have no control over it and it has no added value. It's like a mirror page of your shop.
Your $15 per month could be spend in much better ways. For instance in other places, where it will buy you a REAL standalone website. Many of those sites will give you the opportunity to import your Etsy listings and to synchronize sales. And, as opposed to Pattern, will give you control over its SEO, the option to add other items (ones that aren't in your Etsy shop), personal info, a shopping cart, choose your own payment system, etc..
Plus, the fact that Etsy tricks its users into using Pattern is a big NO in business.
When you click the button to figure out what Pattern is all about, you have signed up! Which is totally unacceptable legally. They never asked you to sign up, they never asked you for information and you most definitely did NOT agree with making payments. Even if there is a one month trial. Very bad business practice!
They might face legal charges on this one.