In which scenario we can use Screen Flow and Sub Flow ?

In which scenario we can use Screen Flow and Sub Flow ?

ANS:  Best example for screen flow is filling the application form which consists of several pages, each page is dependent on the other pages.. if a user is in 6th page and would like traverse to 3 page it is done using screen flows only.. thru screen flows we collect all information and this collected information is given to work object finally...
SUB FLOW: It is to reduce complexity, here we cant traverse once the it is submitted we cannot go back.