# Total energy from KS-DFT: How reliable is it and why?

As the title suggests, my question is fundamental - How reliable are the total energy values from Kohn-Sham Density Functional Theory, and why. I acknowledge that absolute values of energies are useless, but relative values are often used to compute several quantities across different applications. For instance:

1. Atomization Energies - For a simple molecule AB, the atomization energy can be calculated directly from $$E_{AB}$$ - $$E_{A}$$ - $$E_{B}$$.
2. Magnetic materials - Difference of total energy values for systems in different spin configurations (say FM and AFM), can indicate which magnetic configuration is more stable.

To word my question differently: There are many more applications where total energies are used. What I find weird is many research works rarely delve into the validity of this quantity. Why is one able to do this? Note: I also acknowledge that there might be functional-dependent errors in calculation of these quantities, but my question is not about that. Instead, my question is more generic.