We analyze quantitatively the interplay between explicit and implicit renormalization in Nuclear and Molecular Physics. By explicit renormalization we mean to integrate out higher energy modes below a given cutoff scale using the similarity renormalization group (SRG) with a block-diagonal evolution generator, which separates the total Hilbert-space into a model space and its complementary. In the implicit renormalization we impose given conditions at low energies for cutoff theory. In both cases we compare the out coming effective interactions as functions of the cutoff scale. We apply these methods to Skyrme forces for Nuclear Forces and Density Functionals for van der Waals interactions in molecular systems.