Whether you're a designer or not, I think it's important to plan on paper before computer.
Here's some top reasons why I found it's been helpful.
1) Better End Results - This to me, is the most important reason for planning on paper first. Sometimes I have to admit I go straight to the computer before planning anything (especially in a rush) and this has proven a few times to be the worst decision. I always achieve better design results when I have planned away from the computer.
2) More Efficient - Sketching and scribbling gets that overall clear plan and perspective in your head. When you're with paper, you won't be distracted by internet and emails. Also, more often than not you will create several revisions on the computer because something's not quite working and you haven't planned properly - this is also a time killer.
3) Save the Eyes - This is not directly related to the project benefits but general well being. We all know we should be looking away from the computer to exercise the eyes and to take a break from that glary computer, so this is a great excuse to do so.
4) Easily Accessible - You can do this any time, anywhere. Okay, I know there are note applications on our iphones etc but it does feel more set in stone when you physically write or sketch an idea. Your note book can be with you at all times and when that fabulous idea pops into your head - its their to refer back to when you need it.
Conclusion - it's great to use traditional workings combined with technology to best create our end project results.