Graphing with Complex Numbers (2 of 3: Determining the region)

[laughmaker]

This guy is just sensational, an inspiration for every maths teacher!

[rexevan]

I remember learning this during highschool.

[masters.]

I'm not even a native english speaker but somehow I understand everything.
Thanks.

[dominicbaxter]

I learn lots from you so thank you for what you do

[OFaruk]

I don't know what the fuck he is telling.
But still enjoy his style of teaching.

Does anyone know where this is actually used for?
(I know it is for Determining the region but i mean where is it good for in Real Life)