Currently at my house that I bought recently, I have one side of the house draining the gutters down some pvc pipes that end up draining into my sewage line. On the other side of the house, the gutters just drain down onto a side concrete path that butts against the exterior wall of the house. This side is of course not a good way to deal with water, as it can pool against the side of the house. I have a small strip of grass beyond the concrete that I could make a PVC "ditch" to which that side of the house drains to.
Now my question is, in general is it better to drain to the sewage line like the one side of the house, to let it drain down the slope of my yard (which is properly sloped), or to run the water into the street (which I am sure the city may not like so much and I am unsure if that violates any codes)? Is there any harm doing it any of these ways? Is it fine to leave the one side of the house as is, draining into the sewage line?