Not only porn websites need Adult website hosting. If your site dealing with any adult content may need an adult hosting. Here is a list of Adult material types.
If you are running a dating website that not directly posting adult content, but you had a video chat option allowing peoples to chat online by allowing adult chat or allowing posting nudity. A Porn embedded website. Online or offline adult content website. Website which promoting Sex related-materials, books, stories and sex toys. Sexual interaction webcam sites Animation adult content  websites Forums or Blogs which is sharing sexual images, videos etc.