The number of fitting points is related to the dimension of systems and the point sampling methods. Therefore, appropriate reduce-dimension methods are feasible to save the ab initial points. For the weakly bounded complex, the most common strategy is treating the monomers as rigid-body, i.e., to freeze all the intra-molecular vibrations. For a dimer complex, the rigid-body approximation can significantly reduce the dimension of intermolecular PES from 3N-6 to at most 6, where 10 4 to 10 5 direct product grids or (quasi-)random points can still be affordable in gold-standard CCSD(T) level. However, these points will be extremely expensive when the higher corrections, such as higher-order coupled-cluster excitations and the core correlation effects, have to be taken into consideration. More importantly, as significant monomer-flexibility effects have been found in the ro-vibrational spectra of molecular complex, full-dimension calculations that include all the vibrational couplings become more and more important. To construct PESs in both high-quality and full-dimension, the sampling methods must be highly efficient.