SSL/SSH inspection uses certificate inspection
Certificate inspection was chosen because it is easy to deploy. Deep inspection is more thorough and offers better protection; however, it is harder to deploy and maintain. See the FortiOS 7.0 Administration Guide for more details on deploying deep inspection.
Consider your company’s security policies when deciding the need for deep inspection. Typically, deep inspection is needed when content within an SSL/TLS protected connection need to be inspected.