My comments about fingering (no mention of blowing simultaneously BTW) are muscle-memory and coordination exercises. Such exercises have been used widely, not only for trumpet players, but for pianists, recorder players, etc to good effect for a very long time. I just don't understand the "waste of time" comment.
Just as in sports, isolating individual components of the whole of playing an instrument allows the person to concentrate on just one aspect without the distractions and perhaps the tensions caused when doing it all at the same time.
Additionally, the context of the OP's question is practicing scales without the trumpet.