Your gonna get a lot of answers from ignorant people on here. There is no evidence that there are any bad effects, no it doesn't kill brain cells, it actually stimulates them. Smoking marijuana alone will not cause any cancer and will not make you lazy – only naturally lazy people will be lazy. If you have a family history of psychotic illnesses, it could bring it out in you, but marijuana will not cause any psychological illness apart from perhaps depersonalisation. The only reason it is illegal is because the government cannot tax and control it.
Good effects? There are loads – there is no other thing in mankind with as much healing properties as good old weed! Google them and watch the film 'The Union'.
To Connor below, there are no cancer causing chemicals in marijuana fumes as long as you smoke pure weed – weed without any tobacco. You can also use a bong or vaporizer which basically get rid of any harmful chemicals you may inhale.
Suggestion:
There are no good things that come out of smoking weed, smoking weed is neutral as far as affects on your life.
If you smoke you have lung cancer and lung damage to worry about. There are other ways to use weed than smoking it, I advise those methods rather than distroy your lungs.
There actually hasn't been a lot of information out there PROVEN about harm full affects of marijuana on the brain. There are a ton of myths but very little proven fact. As long as you are only an every once in a while user and not a chronic one, you have very little to worry about.
-Connor
