Open Palm, lost art?

[lmeadski]

Being a new ref I watch a number of refs and their mechanics. I also work on mechanics that aren't instintive, like the raised fist for a foul and the raised open palm for a violation. Everyone seems to use the raised fist to signal a foul. However, when I watch senior officials, I don't see the open palm used regularly, especially at the college level (they move right into their signal, such as traveling, double dribble, etc.). I have a terrible time remembering to raise my open palm for a violation. In talking to a few senior officials I work with, they say I should use the raised palm. However, when they don't, it doesn't seem to impact me. I hear the whistle, I know my partner(s) is calling something. Is the open palm truly necessary?