The host thing is a waste and so is the party animal trait.
However, the host trait works if you don't use the stereo or don't offer food, you will still have an epic party. I'm not sure about party animal, I never chose that trait. I have a Sim with max traits, so he has the host trait. The way his house was set up prevented all but one couple of Sims from dancing. For some reason, where I had positioned the stereo made the Sims want to dance in the pantry. The cake, which was the only food he offered was on the counter in the pantry. The pantry was 3 X 6 tiles. In any event, the party guests, all 10 of them, and the 4 people in the house all tried to gather in that one pantry to either dance or celebrate birthday/grab cake, it was a mess. No one could possibly have had a great time as they spent the entire time just bumping into each other and tossing their hands in the air. But at the end of the party it was epic and was going to be talked about around town for years to come. I think this was due to the host trait.
I also had a rock musician that had the host trait and she had parties where she didn't offer food, didn't have a stereo and yet her parties were always epic. Basically, her friends sat around playing guitar or enjoying someone playing the guitar, that was the entire party.
Basically, what I'm saying is that the host trait can be useful in certain situations. Such as, when you are moving up in the politics career track and don't have the money to leave your guests with a great stereo and good food in an awesome atmosphere. But as others have said, it isn't a necessity.
[Edited for correct quoting - Swede]