What friendship is all about ! Having friends have multiple purposes in Pirate Empire: 

1. You can collect up to 40 energy per day from your friends

2. Your friends can speed up you cabin upgrades. Each cabin can be boosted twice and each friend can boost you twice a day.

3. You can send and receive daily gifts from your friends ! Receiving gifts from them also unlocks achievements which give gems !

4. You collect hearts when helping friends ! Those hearts can be used in the frienship shop and exchanged for gifts.

5. You get a friendship bonus when doing Astrologie Elite maps ! So more rewards !

6. Isn't it better to savor a cold beer with friends around ?

I think you got it matey, now get out there and meet some friends !