I have noticed that when I draw digitally, I am prone to making sure every line is as perfect as I can get it. I make sure the color choices are working as perfectly as they can be and that the overall piece is visually interesting and fun. There is much more wiggle room for error and a simple click can easily fix the most basic of mistakes. Truly a benefit of the digital age.
With that being said, I absolutely love drawing in my sketchbook. Nothing beats paper and pen, and there is a sense of freedom I get when doodling the old fashioned way. Sure I mess up, and mess up often, but there does't seem to be as much pressure. My sketchbook is meant for mistakes. It is a place where I can draw whatever and not worry about making it look perfect or cleaning it up for anyone in particular. That's not to say that when I'm drawing digitally I'm a complete wreck. Far from it. I suppose I have simply noticed the differences between the two.
The above doodle is from a page of my sketchbook. There is nothing else on the page except this naked dude. After I drew it I felt is was an accurate visual representation of what I just summarized.
That and its completely ridiculous.