Is it really necessary to learn how to calculate loop diagrams in QFT? In the Wilsonian approach, you only need to calculate tree diagrams. In the loop approach, you have to relate the experimentally measured coupling constant to the bare coupling constant, and I guess the difficulty is doing this to a high order - you have to calculate many loops. In the Wilsonian approach, I guess you still have to relate the experimentally measured coupling constant to the bare coupling constant, but instead of getting it to higher order by calculating loops (since there are no loops in the Wilsonian approach), you have to relate the experimental coupling constant to the infinite amount of constants in front of the infinite amount of terms in the Lagrangian. Which is more difficult, the loop approach or the Wilson approach? Also, which is actually used in practice?