Exocytosis is a process where cells can excrete digested material, but it's also a process where cells secrete other materials and can be a function of communication.
Some cells in the pancreas secrete (exocytosis) glucagen and insulin which regulate glucose levels. When glucose levels rise, beta-cells in the pancreas secrete the insulin.
Neurons send signals via neurotransmitters (in vesicles).
T-cells can send enzyme filled vesicles via exocytosis to prompt viral-infected cells to destroy themselves: a programmed cell death called exocytosis.