All I can say is that there are extreme environmental conditions that alter the tuning of our brass instruments and at some moment, somehow, at sometime you'll have to adjust your slides to compensate if the stage is an abrupt change. Then too, this can't be done in the instant like a "light switch". No indeed, you wouldn't want to hear my solo 5 minutes after I arrived with my trumpet having driven 100 miles through freezing clime, my trumpet in the vehicle trunk/boot. The term "warm up" didn't come into being by the conjure act of a magician. If I can make a quick pass of a chromatic scale, I'll know about as much about the tuning lubrication of my valves and slides as I'll ever know. How well I know the music is another issue.