Yes, offcuts can be utilized again for nesting purposes and cannot be considered as scrap. Thus in utilization percentage the offcuts are also considered.
Check if the "Allow Offcut" setting is ON. Probably, the remaining piece is larger than the minimum offcut size. In such a case the remaining piece is NOT considered as waste.
Quick results concentrate on giving you the fastest optimization. This could be useful if the user is seeking just an approximate value for a particular case, which he wants to convey to a party (say during a telephonic conversation.). optimized results concentrates more on giving you the most optimum solution irrespective of the time taken.
The package will try to utilize the offcuts first.
Note: Offcuts should be of the same material and thickness as the required parts.