There are some clear benefits of l arginine, but there are not too many longterm studies. This doesn't necessarily mean you should worry about the side effects.
Most l arginine side effects will usually depend on your aginine dosage or pre existing medical condition.
If you're a healthy person with no current health conditions then you shouldn't worry too much. However, if you have heart or psychiatric conditions you should consult with your doctor before supplementing.
You can read more about a proper arginine dosage and some guidelines on taking this type of supplement here on the L Arginine Side Effects page.