When the guy working at Mcdonalds gets depressed and starts questioning his real position in life, it interferes with his ability to ask 'would you like fries with that?' with a plastered on smile. So in order for society to function like a well oiled machine, the lowest cogs have been told that being unhappy is wrong. So it depends on who you ask, whether depression can be good or bad. Society will tell you it's bad, because society likes to manufacture worker bees, not realists, philosophers, artists or entrepreneurs. The rewards are not nearly as material or tangible when someone is depressed, compared to having a solid, happy, reliable if maybe a bit mindless, peasant.