I think as you alluded to the fear of using sugar is a hangover (excuse the pun) from the old kit and kilo days, where a large proportion of sugar combined with probably poor quality malt extract led to some unpleasant brewing experiences.
However sugar definitely has a place in brewing. The usual purpose of using it is to increase the gravity while lightening the body of the beer. That's why Belgian beers can be very drinkable while being very strong, they call it digestibility. It can also be used to good effect in something like a DIPA, where you don't want it to be too heavy.
If a recipe asked for brewing sugar I personally would save my money and just use table sugar, you won't taste the difference, and actually you won't taste it at all (which is kind of the point). Muscovado sugar will add some flavours and colour, think of something like a Belgian dubbel or quad, and is good for making dark candi syrup.
My recent Belgian quad had 7% sugar in the recipe, my rye saison recipe is 7% table sugar (scored 44 in a BJCP comp), my silver medal winning Westvleteren clone had a 16% sugar addition (candi syrup made from muscovado sugar), and my gold medal winning Rochefort clone had a 13% sugar addition.
There's a saying about starsan, "don't fear the foam". In this case it's "don't be scared of the sucrose". Not quite as catchy, but you get the point