Sugar is a good carbon source to fatten buds; I use molasses at a dilution rate of 1-2 tablespoons per gallon.
If your buds are wispy and thin, though, you should look to other possible causes as well- the most common are heat stress and light leaks.
Sugar is useful but like other sources of carbon, if your grow environment is poor, its value is negligible.
A carb synthesizer such as Sweet has the catalysts to improve sugar usage by your plants.