Almost all websites can use CloudFlare. CloudFlare works for both static and dynamic websites.
CloudFlare is not suitable for websites that stream video or audio directly from their origin server. If a website uses YouTube or Vimeo then it is compatible with CloudFlare.
Examples of websites that greatly benefit from CloudFlare include:
Popular websites that get heavy visitor traffic
E-commerce or business sites
Sites with diverse international traffic
Sites under DDoS attack
Sites with heavy server load
Sites with past security breaches