Each to his own! In this case, however, the sole purpose of the plugin is to widen the stereo image - not to add something to the sound. The idea is that a trumpet is still a trumpet, it just takes up more space in the stereo field. This plugin can "almost" do that, unlike a typical chorus effect that is supposed to turn one trumpet into 10 trumpets or a typical echo, which changes the musical meaning of your music (melodies don't always lend themselves to being echoed).

As a sound-engineer I've also found that music, since its made up of complex sound, benefits from sounding simpler, when played through a mono source. In other words, music benefits from less chorus, less reverb, when played in mono. It makes everything clearer and easier for the listener. I use phase-cancellation as a tool to improve the sound. To accomodate people who listen in "mono like" enviroments while giving other people the satisfaction of fat stereo.

Could you re-name the controls according to their function? (Instead of Stereoizer-Knob, Stereoizer-Slider)

But would the affected voice (or whatever) not become quieter when played from the mono source?

It works by adding a phase-inverted, slightly delayed, discrete chorus to the dry signal.

You mean like this: