I just found a good tutorial on regions. ANYONE thinking about mapping for JO should read this, especially if you're decent at Jed and can't get by without layers.
The drawback to regions is that you can't save them like in Jed. But - they seem to be easier to select. Basically, you can make a region by dragging a brush around the area you want to work on, then click Region - set brush. Or select the brushes you want, and click Region - set Selected Brushes.
You can now work on this area without the rest of your level cluttering up your view. Another great use of regions is that you can compile the region by itself. This can mean the difference of a few hour compile time vs. a couple minutes.
When you're done working with that region, click Region - Off, and you're back to your full map.
heh I guess I should give the link :p
http://www.geocities.com/halucinating_monkey/region_tut.html)