original_query: What is the significance of integrating out high momenta or high energy in momentum-space RG practitioners' theories?
query: What is the significance of integrating out high momenta or high energy in momentum-space RG?
answer: Integrating out high momenta or high energy in momentum-space RG is analogous to coarse-graining in real-space RG.  It results in a focusing on larger length scales and the suppression of contributions from short-length scale fluctuations.