I like machines for some bp...not all. The batters can get the timing and rhythm easier off a pitcher. A machine is good for building the quick twitch/reflex muscles. But IMO it should be a combo of front toss, machine, and a live pitcher.
I don't think it's terrible to use a machine as one part of a regular series of drills.
However, I do think it's a terrible idea to base your cut/no-cut tryout decisions off how well a girl hits off a machine. As Amy and others have pointed out, it can paint a false picture. I'm just a parent, but even I've seen plenty of girls whose performance off live pitching differed substantially (good and bad) from their performance off a machine. I've never seen a good live hitter who was unable to hit front toss. JMO.
Basing a decision to cut or keep a player on hitting off a machine alone is foolish and shows a coaches lack of knowledge on hitting mechanics IMO.