How are chemicals prilled?
I don't know the answer for sure, but will take a guess based on what I read at the link provided by Mithoron.

Non-chemists outside the laboratory, and persons who have to handle and work with those chemicals would certainly benefit from prilling to reduce dusting which could be detrimental to their health in breathing and on the mucous membranes.

Gardeners use Ammonium, potassium and calcium nitrates in fertilizers and stump removers, and do not always wear eye protection or dust masks. Thus prilling helps to mitigate exposure to these chemicals.