Optimal structure for an ecommerce multisite installation

I have an ecommerce project using WordPress Multisite. My question is about the pros and cons of multisite setup.

I've done enough ecommerce to know that the Wildcard SSL certificate for the sub-domain structure (site.domain.com) is significantly more expensive than it would be if we use the path (domain.com/site) setup.

It's also my understanding that using the path setup is superior in terms of search engine friendliness.

So it appears that choosing the path structure is by far the best choice... but wanted to ask the WPMU community if I'm missing some advantage to setting this up using subdomains.

What - if any - are the advantages to setting multisite up using subdomains?