Smoking moldy weed can put you at risk of certain health hazards. Inhaling the mold spores is the main issues and can cause damage to the lungs. Some people can have an adverse reaction to the mold, particularly if they are otherwise sensitive to it. Generally, however, people will experience coughing and throat irritation when they smoke moldy weed but will not suffer any other adverse effects.
More serious symptoms arise in people that are extremely sensitive or allergic to mold who might then suffer from a fungal infection in the throat or lungs. Some of these lung infections can become serious and some studies have shown that these invasive fungal infections are more prevalent among cannabis smokers than the general population. Overall its probably better to err on the side of caution and avoid smoking weed that is moldy.