"Extra sweetness" refers to an additional level of pleasantness or kindness. It means going above and beyond what is expected or showing extra care and thoughtfulness towards others. Full definition
The great thing about this recipe is it has the creamy, smooth texture of applesauce, but the deliciously sweet taste of strawberries with just a hint of honey added for extra sweetness. (wholehealthhacks.com)
I'll probably bring some honey or brown sugar cubes with too - just in case anyone wants me to stir in a bit of extra sweetness at my family's holiday dinner. (alyssaandcarla.com)