Actually, the saying is that you should never go to bed angry. Some relationship counselors will tell you that indeed, you should always clear up the air and not go to bed angry at each other. For some people, this works.
However, other counselors will tell you that there are some instances wherein it might be better to let things sit for a while. Sometimes, people need to sleep on issues in order to sort things out.
The answer, then, depends on the individuals involved. It also depends on the issue and the circumstances surrounding it. At the end of the day, you and your partner will be the ones to make the decision.