Lithium trisiamylborohydride is primarily used as a selective reducing agent in organic synthesis. It is particularly effective for the reduction of sterically hindered ketones and esters, where other reducing agents may fail. Its application is crucial in the synthesis of complex organic molecules, including pharmaceuticals and fine chemicals, where precise control over the reduction process is required. Additionally, it is employed in the preparation of chiral alcohols and other stereospecific compounds, making it valuable in asymmetric synthesis. Its ability to operate under mild conditions further enhances its utility in sensitive chemical transformations.