Can low cholesterol be bad for you?

This question is actually about my husband, as I worry about his health.  He is 41 years old, weighs about 215 pounds and is 5'10" tall.  He finally went to the doctor for the first time in about 10 years for an ear ache.  The doctor did standard bloodwork and checked his cholesterol.  The first time the results came back, the doctor thought they made a mistake and had my husband re-tested.  Again, his results came back as an overall cholesterol of 91.  I've read articles that cholesterol that is too low is also bad for you and tried to explain to my husband that he should follow up with the physician and ask more questions.  I have to add that he drinks alcohol daily (6-9 beers) and smokes pot several times per week.  I'm worried that he is going to ignore something that may be important, just because his bloodwork says that his cholesterol is "great".  Any advice is welcome.
Thanks.

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While high cholesterol levels may indeed be warning signs of many health issues, it does not logically follow then that all cholesterol is bad and you should try to wipe out any cholesterol in your body. We need cholesterol to build and maintain cell membranes, for production of sex hormones, to aid in the manufacture of bile (which helps digest fats), and to convert sunshine to vitamin D. Cholesterol is also important for the metabolism of fat soluble vitamins, including vitamins A, D, E, and K. Check out How Stuff Works: Cholesterol to find out more about the role of cholesterol in our bodies and the many important functions it performs. Also, low cholesterol may be signs of other conditions, hyperthyroidism, liver disease (may be alcohol related), maladsorption, or malnutrition. Also, HDL (High Density Cholestrol) is the good Cholestrol and it helps remove LDL (Low Density Cholestrol) the bad one, from the walls of the blood vessels (plaque) that can cause heart disease.