Leica or Zeiss invented ED glass, a very long time ago, and put it in camera lenses decades ago.
If you use the scope for photography, yes.
If you use the scope to see tiny details at high magnification, yes
If you spot large game with a 20x or 30x 65mm or 80mm scope, no, you don't need ED, but you still need a high quality scope.
If you put Swarovski 80mm side by side, HD vs no-HD, at 20x on a cloudy day you see no difference. At 40x on a sunny day, you see color fringing through the non-HD model. They are both great for finding deer or such, but the HD is better for observing some tiny feather detail on a distant bird.
There is no difference in brightness, just in how detailed and well resolved the image appears at high magnification on sunny days.