I always thought that having someone "on point" - ahead of the towplane - was not primarily to relay signals from the wing runner but was done to monitor the area behind and out of sight of the wing runner for anything that could interfere with the launch and to stop the launch if that happened. I've only seen this happen once in my fifteen years of soaring though and when you come down to it if this was really important you could just have a person stand behind the wing runner to monitor that area.

It's SOP at my club when we have enough people at the field to have someone to do it. It has occurred to me that it does introduce the possibility of the person being hit my the glider or towplane if one of them swings exceedingly badly (to the left in our case) but has this ever happened anywhere? We have a very wide grass field and almost never have any significant amount of crosswind component so our experience probably isn't typical.