Agreed, it also give a sense of character development that normally wouldn't be there, as the character is just reclaiming their lost self. Great for either the plot, OR if you're to lazy to develop a character in any way. XD I hope it's for the sake of the plot.
Also, I feel that making a hot head and a sarcastic jerk work together creates some interesting quarrels.
Your last point I have an example for: May and Drew in the anime.
Couldn't a death of a close person also shape character growth?