Interesting - I've been there and had it backfire, but not in the way you think.
I wanted a PA for the entire season, but if I hired a friend, I would only have them for the 1st half and have to hire someone else for the 2nd half. Or I could hire someone I didn't know and have them all season long. I was talked into hiring my friend. She was amazing, but the person I had to hire for the 2nd half of the season was awful. (Though one never knows if the season-long person would've been good or not.)
In other cases, I have hired my ASM from the ballet for two different jobs/companies (one as my assistant PM and another as a technician). Both times she's been amazing. And it's been really helpful in making me feel more at home in new places, by having her around.
While having a friend with similar styles/philosophies is appealing, you never know what fresh, new ideas come from hiring someone you don't know.
It's a crap shoot either way.