Disadvantage of Subdomain

SEO challenges - There are some benefits of SEO in subdomain but there are some challenges also. If you are using too many subdomain so you might face difficulties to rank each domain. Your main source of traffic is SEO then subdomain is not for you. Subpages is best option for you.
Branding issue - Too many subdomain let visitors confuse and they might loose their interest and it is not good for brand.
Navigation problem - User face difficulties in navigating content on different subdomain.
Difficult to Maintain - For small business it is difficult to maintain subdomain with limited resource.

Sumit