We optimize sites with a US audience in the same way as all other sites, meaning that content that passes through our engine is optimized regardless of where it is served next.
Of course, we serve this optimized content as close to the user as possible via our CDN, which covers nearly 220 points of presence around the world. So no matter where the user is located, there is optimized and cached content ready to be served.
When we integrate our solution to a site, what matters is that the origin infrastructure is as close as possible (in a network meaning). And this is the case for the majority of the sites we encounter.
In the particular case of Salesforce Commerce Cloud sites, the pods are generally located in Europe, 10 ms away from our servers, so there is no latency problem.