We don't keep anything near the concrete curb in the garage, so there's no trip hazard. It's the wife's garage, so we just use it for parking. You do need to pin it down, though. Before I did, the wife would hit it at an angle and move it. I got tired of dragging it back in to place over and over.
In our case, if the car went through the back of the garage, you'd go down a small hill until the trees stopped you. It would certainly mess up the garage and car, but you'd be unlikely to be seriously hurt at parking speeds. If there were a house on the other side of the wall, or a cliff or some other hazard, I'd use steel pipe bollards filled with reinforced concrete.
