In the second chapter of Understanding Molecular Simulation, Frenkel and Smit derive an equation for the partition function and the thermal average of the generic observable A, stating that these equations "are the starting point of virtually all classical simulations of many-body systems".
I understand the theoretical significance of the partition function, and I can see how, in theory, by knowing the partition function one would know the energy of the system, and if I'm not mistaken, also all the other thermodynamic quantities one could be interested in.
What leaves me confused is the practical use of the partition function in the computational chemist's work. I have some experience with running simulations with programs such as LAMMPS and GROMACS, and yet have never had a real first-hand encounter with the partition function. Is it used by the programs to compute the thermodynamic quantities they output? If so, would it be possible to provide a general description of how this is done?