The use of recreational marijuana does affect ones health. It is not good for a persons lung even if only used once in a while. The definition of recreational can also mean once a month or once a day. The more a person uses the more affects it can have. I do believe it is a personal choice to harm ones health using drugs.
As far as short term effects are concerned, they're generally limited to general lightheadedness, increased heart rate, lowered blood pressure, loss of coordination and short term memory loss. While light marijuana use is arguably "safer" than smoking cigarettes or drinking alcohol, it is not completely safe. You're still inhaling smoke, which can lead to emphysema, heart disease and cancer, just like cigarettes. Not only that, but marijuana use has been linked to sterility in men.
Using marijuana relaxes the nervous system which could slow down a person's response time. This could be detrimental at work or school. Marijuana can also decrease the strength of the immune system for some, which could open the body to other infections and sicknesses. Since it's impossible to know if a person will become addicted to marijuana until the person starts smoking it, recreational use could turn into a serious problem and lead to more serious drug use.
This is a natural plant that has been used for a long time. Recreational use should not cause effects to your health. It is prescribed by physicians for daily continued use for several different health problems. I think using marijuana where it is not legal would cause more health effects due to stress from worrying about getting arrested than the actual substance itself.