1) He can solve our goalscoring problems and keep us up.
2) He is worth the wages if he does this.
3) He will excite fans who had become a bit disillusioned by our unexciting football.
4) He will lift the mood of the camp and will hopefully give fans a good reason to continue to go and watch home games.
5) He will be a great mentor for Wickham. Bags of experience and that will rub off on the young lad.
6) He will inspire others around him to create more chances when they see his pace/movement.
7) He can influence the team by showing them how it's done and bring some confidence back.
8) He is a superstar and popular around the world, he could make a move to Sunderland more attractive for London-obsessed players. Many players would be attracted by the prospect of playing with him.
9) He will bring lots of outside attention to the club and the media will be more interested. That might lead to England scouts/Hodgson being more interested too. Which would benefit our other English players.
10) He can help to inspire the young lads in the team and academy players who would see him as an icon/role model.
I can think of a few more but that's enough for now.
It's not just about whether he can be amazing for 3 years. There's lots more positives than just the goals he might bring too. Someone like Altidore (bless him) was never going to have this kind of impact. In fact, Altidore was having an extremely negative impact. What Defoe brings us is goals, positivity and that superstar factor that we've not had for a long time.
This could be a massive turning point for this club.