Potassium chloride is not directly used in pyrotechnics, but can be used to make other pyrotechnic chemicals such as Potassium perchlorate and Potassium chlorate. It is used to turn NaClO4 into KClO4 and NaCl (see Preparing perchlorates). it is also used to increase smoke density in very small amounts; mainly to potassium chlorate based smoke compositions.
Potassium chloride is sometimes used as a water softener salt, instead of NaCl (check the label). It can be bought at hardware stores and grocery stores.
KCl is not particularly toxic or dangerous.