So as far as I can tell the only good affect of marijuana is the release of dopamine. However dopamine is not meant to be absorbed in large quantities like weed does. Furthermore there are much healthier ways to release dopamine such as riding a bike or playing sports. Even reading a book releases dopamine. While we are at it here are some more affects I found in my research:
Feelings of panic, anxiety and fear (paranoia)
Hallucinations
Increased heart rate
Trouble concentrating
Decreased ability to perform tasks that require coordination
Decreased interest in completing tasks
sourceSo what is good about marijuana again?