Gutter screens are optional. The purpose of a gutter screen is to block bigger debris such as large leaves from entering the gutters and clogging them. Essentially they decrease the amount of times you will have to clean your gutters each year. Just make note that most gutter screens still allow tiny seeds and dirt to enter the gutter which could build up and result in blockages within the gutter as well. When choosing gutter screens, be sure to choose one that is easy to remove and also to reattach.