Most all grain recipes don't use sugar - as the name suggests, its all grain !!
Some recipes do add a bit of sugar but most I've seen which include some sugar have been clone recipes of well known commercial beers. Has usually been explained that commercial breweries have used sugar in some part as its cheaper than grain and makes for more profit. Therefore if brewing a clone and wanting a close result to the original commercial beer you would add sugar to replicate the original as closely as possible.
If I was adding sugar (I never have) to an all grain recipe I would add it slowly towards the end of the boil or even just into the fermentation vessel before transferring my wort in on top from the boiler. I suspect if you dump it all into the boiler in one go during the boil you could risk a foaming messy boilover!
What recipe you looking at trying out of interest ?