Never, ever have an exposed sidearm if you are CCW legal, for both tactical and legal reasons. It's a bad practice all around.
Never??? Quite to the contrary, I find many situations where open carry is ideal. Like Edward, who posted above me, I've diffused s situation or two by having a handgun visible on my hip.
I carry openly at least as much as I conceal, and in hot weather (I'm in Az) even moreso. In colder weather, a jacket makes concealment pretty natural.
And speaking of "never", I "never" conceal in the field. Big hanguns for field use pretty much dictate open carry for me, and a "little" handgun won't do the job I need when I'm hunting or woods bummin'.
There are a few places that I habitually carry concealed; banks, Wool-Mart and other sheeple gatherings, and so forth. For the most part though, I've been open carrying since before CCW began as a new trend in the early 90's, and it still works just as well.
After 25-30 years of open carry, and having been CCW legal for 15 of those, it just doesn't much matter any more one way or the other. It's just another tool, like a cell phone or Leatherman tool that I wear in case I need it. Whether anyone else can see it or not doesn't matter much to me most places I go.
In the end, it's just another way to carry something that might be needed somewhere along the way.