There is extensive documentation on the internet from fantastic brewers such as Jamil Zainasheff who have used amounts such as 3 lbs of regular cane sugar in a 6 gallon recipe that has placed in the second round of the National Homebrew Competition. I am not trying to be a Jamil fanboy, I am merely stating that you don't take home gold medals with beer that tastes "cidery" (Source: The Jamil Show, Belgian Golden Strong).
There is also the advantage of using simple sugars in high gravity fermentations in order to make them attenuate properly. In this case of extreme fermentations (I would estimate around the 1.100+ area) it is best to "step" your fermentations. For example, allow the yeast (don't forget that healthy pitch!) to consume the maltose-based sugars first and then when the gravity has dropped, start dosing with the simple sugars. The point of not adding all the fermentables at first is because it will overwhelm the yeast due to viscosity of the wort and because the yeast will choose to metabolise the simple sugars (glucose, sucrose, fructose) in preference over the maltose. These latter sugars (which come from the malts) will be left unfermented, resulting in cloying sweetness and a heavy body.
(Source: Sean Paxton's Dogfish Head 120 minute IPA clone recipe).
As mentioned, hoppy beers may benefit from simple sugar additions to dry out the malt backbone, leaving the hop characteristics (bitterness, flavor, and aroma) more pronounced. Again, you want to make sure of balance in the recipe (you still want malt!), but you don't want all those expensive hops covered up by residual sweetness or body that may not mesh well. Make the most of the hops during this time of record prices by getting your beer to ferment drier, leaving a pleasant hop tone to the beer.
(Source: 2008 Samuel Adams Longshot Winner: Mike McDole's Double IPA, aka Pliny the Elder clone).
Don't be duped: sugar has its place in beer by making it more digestible and easy drinking, when used with a solid and balanced recipe.