It depends.
A mock meet is basically a testing day, as well as being tool to directly train for a comp day. Throughout my programming I can track various measurables to gauge progress, but there are some things that you can only test in a more controlled setting than a normal training day. One example would be the testing of a 1 rep max. I'm also interested in top end form and weaknesses, and to expose these in the most relevant way for powerlifting I need to test with heavy singles.
For true 1rm testing I'd want to be fresh and basically completely recovered from fatigue, but for everything else it doesn't matter even if I'm massively suppressed because even those slightly lighter weights that I'd end up lifting will expose the same limitations. It's also possible to manage fatigue levels and track these 1rms tested while fatigued.
Tomorrow, for example, my performance should be quite suppressed.