Firstly, if 50% Humans shifted to the Moon, Moon may have to bear with a lot of noise, it may not like this.
Secondly, if 50% Humans shifted to the Moon, Moon may get very busy, it may forget to blow tides on Earth.
Thirdly, if 50% Humans shifted to the Moon, Earth may actually feel relieved, it may give Moon best wishes.
Fourthly, if 50% Humans shifted to the Moon, other Moons may come to see what is actually happening, our Moon may start showing off.
Fifthly, if 50% Humans shifted to the Moon, Humans may start mining the Moon for precious metals, Moon may not look the same anymore.
Lastly, if 50% Humans shifted to the Moon, even Aliens may start to move in, Moon may start sinking.