Haven't received in-game bonuses, and I'm not sure how they work.
For information on how to link accounts, visit our Recruit A Friend article.
Linked players can summon each other once every 30 minutes if their characters are on the same realm and faction. To summon your friend to you, right-click their character portrait and select Summon Friend.
Note: Death Knight, Demon Hunter, Goblin, Worgen, and Pandaren characters cannot be summoned until they complete their starting experiences.
The recruit is granted an Extra-Spacious Knapsack for any character which completes the Exile's Reach starting experience. The bag can be claimed from the character's mailbox after they complete the final quest and leave Exile's Reach. Because Death Knights, Demon Hunters, and Allied Race characters have their own starting areas, they are not eligible for the Extra-Spacious Knapsack.