/ic/ - Artwork/Critique

I'm confused with perspective, but I don't really know how to explain. I guess it goes something along the lines of "Do I have to use perspective into every single drawing that I make?"

If I want to draw this woman for example, do I have to somehow find a horizon line and vanishing points? Vilppu says that we can construct everything from boxes, so do I have to "blockify" this woman (or whatever it is I am going to draw) before actually drawing her? and how can I be sure where the horizon line and VPs are? Then there is one exercise with a bunch of boxes stringed together seen from a difficult angle and I just couldn't figure out how to find their vanishing points or how they connected to the same horizon line.

In this video (https://www.youtube.com/watch?v=QBv5z0Y2odE)) the guy draws a piece of paper in perspective and then draws a bunch of them, do all these sheets have their own vanishing points over different horizon lines?