Well, in some crossovers, the friendships are really cool. Imagine Naruto characters interacting with the Fairy Tail crew at the guild hall. They might exchange stories about their respective worlds. And the character development can be quite unique. A character who was shy in Naruto might become more confident after being influenced by the Fairy Tail environment.
One interesting aspect could be the unique magic and jutsu combinations. For example, a character from Fairy Tail might learn how to use a Naruto - style shadow clone jutsu in a creative way during a battle. It could also be interesting to see how the different power systems interact, like when a Naruto character tries to adapt to the Fairy Tail guild system.