4-Bromophenylhydrazine hydrochloride is primarily used in organic synthesis as a reagent for the preparation of various heterocyclic compounds. It is particularly valuable in the synthesis of indoles, which are important structures in pharmaceuticals and agrochemicals. The compound is also employed in the development of dyes and pigments due to its ability to form stable intermediates. Additionally, it serves as a building block in the production of biologically active molecules, including potential drug candidates. Its role in coupling reactions and as a precursor in the synthesis of complex organic molecules makes it a versatile tool in chemical research and industrial applications.