1) setting boundaries helps others (and yourself) make sense
Making sense is a best way to enable action. The opposite is also true, confusion will lead to inactivity. How will anyone be able to tell one grain of sand from another, without you drawing a line for reference. If you want people to read what you write, but what you sell, or help your project out, your line can make it easier for them to do so. If you don't draw your line, no one will notice. Why should they?
It's good for you as well. It will also help you decide on what actions to take: who will you work with, what project will you take on, knowledge and skills will you invest in?
2) Your boundary can (and most likely will) change
No need to make your line in cement. The world is constantly changing, and that will trickle down to the stands you'll take. Those that can adjust to change quickly have an advantage over those who cannot. Sand makes it easy to move your line.
In some ways, the act of drawing the line will matter more than where the line goes - in the same way plans are nothing but planning is everything. Chances are you will learn a lot just by deciding what to include and exclude on your side of the fence.
What do you think? Where will you draw your line?
ps - if you're interested in signing up for Paul Jarvis' mailing list, click here.