Both MIP optimization and populate generate a series of solutions, but the two procedures differ in their aims. The aim of MIP optimization is optimality: after a solution has been found, MIP optimization will generate only solutions of improving objective value, and the procedure will stop when optimality has been proven. In contrast, the aim of populate is to generate as many solutions as possible: after a solution has been found, populate may generate solutions of both improving and degrading objective value, and it will stop only when it cannot generate any additional solutions or because other stopping criteria intervene.

In order to decide which procedure is better for your application, you should first try the MIP optimizer. If the solutions produced are sufficient for your application, then the MIP optimizer is the appropriate choice. If not, then you should try populate to generate more solutions and to have more control over the properties of the generated solutions.