AD campaigns?

Advert test
for some its a waste of money. esp. if you don't know what you are doing
for some it's a money earner. esp. if you are smart, test and optimise

what's with the vague questions ???
Im just trying to gain as much information about a topic before I go waisting money I dont have . Everyone has a different view on the topic for me the best knowledge I can get is through references.