The average lifetime of computer hardware is a few years, the time between new versions of software is even less. As computer programs evolve they become easier to use. This effectively means that you no longer have to be a highly trained theoretician to run even quite sophisticated calculations. It is quite easy to run a series of calculations which produce results that are absolutely meaningless. The program will not tell you whether the chosen method is valid for the problem you are studying.
Quality assessment is thus an absolute requirement.
This, however, requires much more experience and insight than just running the program. Basic understanding of the theory behind the method is needed, and knowledge of the performance of the method for other systems. If you are breaking new ground, where there is no previous experience, you need a way of calibrating the results. You just pick the number closest to experiments and claim that you can reproduce experimental data accurately. There is thus no clear consent from theory.