I don't expect GPS to better than 15' accuracy, although sometimes it is. I rarely get closer than 50' to anything, just to be sure. The home point only matters for elevation, as the home point is the only reference it knows for elevation. Everything is based on home point elevation, so always launch from the same point.
After I triple check my mission waypoints, when I fly the mission the first time, I always keep a close eye on the bird to insure safe margins of error in the flight path. After this first successful flight I don't worry about it much, however I always have my finger on the mode switch to pause the mission if I see something strange happening. I will only fly the mission at night after I've had several consistent daytime flights without problems.
After I triple check my mission waypoints, when I fly the mission the first time, I always keep a close eye on the bird to insure safe margins of error in the flight path. After this first successful flight I don't worry about it much, however I always have my finger on the mode switch to pause the mission if I see something strange happening. I will only fly the mission at night after I've had several consistent daytime flights without problems.