Cannabis is a drug. Drugs are useful for many health conditions. In the case of Cannabis, it can;
Relieve anxiety
Improve eyesight (when you have glaucoma)
Reduce pain
Treat certain other medical conditions

Cannabis is also used "recreationally" and depending on the dosage has similar effects to alcohol or nicotine (depending on the strain)

The health risks of cannabis are similar to those for both smoking and alcohol as well;
Lung damage from inhaling carbon
Liver damage from high nickel content
Short term memory loss from oxygen deprivation
Impaired judgement
Fatigue
Reduced motor skills

Based on the risks and rewards, it's your call