OK, I know. I get it.
Constructions and perspective grids are not the funnest, sexiest parts of making a piece of art. There's always a real temptation to skip this step and get right to the good bits of doing the drawing.
|The little X is to remind myself which of these lines was the horizon|
If you take the time to carefully plan your drawing, you're less likely to have the artwork turn out wonky, or end up having to erase and re-draw a bunch of stuff because you accidentally used two different points of view on the same composition*
* and before you say "what about cubism" these rules apply double, or triple in that case, because each of the different points of view presented has to be consistent with itself.
It also helps to establish the settings of your drawings as a real place that people could visit.
When I'm doing constructions I mostly just hint at the location. I lay down the framework so that when I do the detailed illlustrations later, I have a basic idea where the characters are in the setting, and what details need to be added to create a sense of place.
If your viewers believe they could really go to the place where your characters are, then it will give them another way to connect with your story. At least, it seems that way to me.