Hi Sandy,
They are damn heavy, I tend to use them when the water is really cold or pushing a bit, heavier fly = slower swing. When I need to get a fly down very quick like necks of pools they are also useful. Also worth considering is thin plastic tube with either a cone or a few tungsten beads incorporated somewhere.
Above about 1" they can be a bit of menace depending upon the line you are using.
Cheers
Ben