I disagree. sometimes it's a great way to light the mood or just for a break in a main champaign. One of my old groups did something like that. I DM made characters for all of us that where totally outside of what we were used to playing. It was only for on night but we all had a good time nd it did challenge all of us. We agreed it was good for all of us.
Q: How many Call of Cthulhu players does it take to change a light bulb?
A: All of them, because you never, EVER split the party!
God grant me the serenity to accept the things I cannot change, the courage to change the things I can change, and the weaponry to make the difference.