Porn is bad in the sense that it can create false expectations between what seen and reality. People seeing porn might have a false understanding of how sex works. In terms of time and actions that the partner might maybe not want to take. Some even form a connection between watching porn and sexual reaction which then negatively affects their reactions to real sexual actions. Together with the bad effects, porn may be helpful in teaching teenagers about the process, mainly in conservative societies where the subject is Tabu. This although will be beneficial only if the person bears in mind that the images don’t reflect reality.