Wouldn't it be nice to focus only on what you care about? You can do just that in the AE world. Why preview the entire comp window when it is much faster to look only at the part of your composition that interests you. Here's how.
Enable the Region of Interest by clicking on the small icon next to the resolution menu in the comp window.
Drag out the area you'd like to see.
When starting a preview, only the highlighted area is seen.
To exit, click on the Region of Interest icon again.
Using Region of Interest has no impact on your rendered file.