Pros: momentary relief from the world, brief window of elation, temporary elevation of things (even if a mirage).
Cons:
Depression
Anxiety and panic attacks
Terrible effects on health
Holds us back from our potential as human beings
Keeps us from accomplishing goals
Keeps us from even developing goals
Expense
Skews our perception of reality and those around us
Makes us misinterpret others and their intentions
Puts us on edge
Helps us develop a poor opinion if ourselves
Puts us at risk for a slew of diseases
Potential for bad behavior we regret
Overall puts a dark pall on our lives and robs us from a true and real life.