Most people believe that studios earn money by selling their shows to TV stations; this can't be further from the truth. In fact, studios need to pay TV companies for timeslots. Most studios earn money by selling figures, DVDs, and other merchandise related to their shows (this is why conventions are such an important part of the industry). Because of this, it is a studio's best interest to keep viewers attached to their show even after airing. Extra content plays a huge role in this.
If you've stuck around the community for some time, you'll notice the existence of OVAs. OVAs are episodes that have been unaired and are released exclusively through DVDs, usually some time after the original show has finished airing. These OVAs often convince people to buy DVDs (usually with a decent amount of fanservice ( ͡° ͜ʖ ͡° )), but a large portion of fans will watch them for free through unofficial streaming sites. Nevertheless, this is also helpful to the studio because it renews the people's interest in the show and will increase the possibility buying its merchandise.
Another important extra content is music, namely the opening, ending, and the soundtrack if they are especially good or made by a popular musician. Anime is and was never mainstream in Japan. However, openings and endings will be frequently sung by popular artists and may convince listeners to watch the shows. The most recent one that I remember is Sugar Song to Bitter Step, a great ending song made by UNISON SQUARE GARDEN for Kekkai Sensen (Blood Blockade Battlefront). This song was the number one in JPop charts for a while, and I'm sure that it brought a few listeners to watch the show. Love Live albums also reached number 3 at their prime; however, anime exclusive songs reaching so high in the charts is quite a rare occurrence. Another role that anime music could have is keeping fans interested in the show. This is just an assumption that I made, and has no statistical evidence. However, I don't know about you but I still get hyped after listening to the Baccano opening and replaying the opening in my mind (season 2 pls).
Nowadays, a lot of work is also being done by streaming sites such as Funimation and Crunchyroll to keep viewers interested in their shows, such as dubs and podcasts. There's also tons of other extra content such as studios uploading content to YouTube and coreleasing DVD and manga. Some people hates these extra content, calling them cheap advertising and marketing ploys. For me, all that matters is that the industry stays alive and interesting. Whatever it takes.
