Did you know that using the "Master Tempo" on your CDJ ruins the sound quality of the music you play ?
Not only it lower the dynamic of your track, but also creates audio aliasing over melodies, pads and pretty much everything in the song. What it does is, when you pitch up or down your track, it time stretch the music in real time to keep the original key, but resulting to unnatural audio result, just open your ears 👂
So you probably uses it because you want to mix in key, and as much as I can understand the concept of its use, but if you care about the sound QUALITY over the "mashed potatoes squashing audio", you should definitely stop using this option. (goes the same with Ableton "Beat" mode, go for the "re-pitch" option !)
Because back then, on vinyl, you couldn't use master tempo, as there simply wasn't any, and nobody needed it ! 😉