Previous research has suggested that people who sleep seven to eight hours a night have the lowest rates of heart disease. However, there has been little direct evidence that getting a good night's sleep can help ward off a cold.

It's "obvious" that not getting enough sleep is bad for you, but without research like this, we don't know in what ways or to what degree. Otherwise, sleeping to prevent a cold is as "obviously" good for you as hanging garlic around your neck or taking large doses of vitamin C.