The act of simple knows best wins the race with art, the process of drawing quick to capture ideas is essential in the fantasy art industry and simplifying your art in this process helps you along.
Reducing the quantity of lines and shading can make your drawings appear empty, but most of the times this is the desired effect you want to achieve, because all you should really care about are new ideas and concepts you can build on.
By simplifying your art along the way you allow for quicker and faster quality results to emerge in your own art style and drawing more ideas helps you create more possibilities.
An example that best fits what I am talking about is if you look at a cartoonists work, now I don't know if you have ever seen a cartoonist draw, either up close or on television, but they often just start to draw with marker pens and just sketch spontaneously and just seem to know what they are drawing before they have finished drawing it, characters just seem to trip off the pen and faces and expressions and all that quick drawing of lines relates to simple but professional looking work.
3 Tips for making your drawings simple, but effective:
Draw fast and sketch quicker - Knowing what you want to draw is the key, then next you can draw fast to capture it and often the quicker you draw the more energy your art will have, useful for drawing characters in motion or action.
Lose the detail, details are only for your finished drawings, detail just gets in the way at this point and it can distract from your main goal or purpose when focusing on your drawing.
Always have a couple of sheets of paper to sketch ideas out before hand, test the quick sketch method on these sheets and see what ideas you can speed draw...oh and time yourself too, this is all about making your time more effective and useful.
Remember if you always plan to draw quickly, then you will become a better artist at planning other aspects of the art creative process and you'll certainly be a better artist because of it.