I have a neighbor who does this, and it seems fine. There are much worse tripping hazards on the block. It's a midsize apartment building, and she runs a cable out the window. I would consider it a real hassle, but she doesn't seem to worry too much about getting "her" spot. I think it's just opportunistic. If it's available, she'll plug in. I guess if there were 40 cars plugged in on the block, that would not be ideal, but it seems fine at this scale.