We study the formation of Cu2ZnSnS4 (CZTS) films from various liquid-phase precursors. Our experimental data point to the significant role that reactivities of precursor components play in the quality of the final material. Although reactive molecular precursors favor formation of CZTS under milder conditions, the formation of large crystalline domains requires using less reactive nanostructured precursors. We explain this effect using kinetics of nucleation and growth. We have also demonstrated a strategy to effectively enhance grain growth of CZTS using solid-state phase transition as the driving force for nanocrystal sintering. We hope this contribution will provide a useful guide toward the rational design of liquid-phase precursors for inorganic semiconductors for electronic and optoelectronic applications.