The expressions for the minimal work of aggregate formation as a function of the aggregation number and monomer concentration for a system with a limited number of monomers and a fixed volume have additional terms in comparison with a bulk metastable phase. The role of these terms has been analyzed in the case of droplet homogeneous nucleation and micellization in a nonionic surfactant solution. The appearance of the potential well and direct and reversal aggregation barriers in such systems and their dependence on the system parameters and monomer concentration have been considered and compared.