I've run across a few people recently that had no idea what the outline mode was for Illustrator. This is shocking to me. It's one of the defining features for the program and makes editing lots of layered shapes quick and easy. To use outline mode hit cmd + y. You will see all the colors and filled shapes turn into outlines only. In outline mode there is only one way to select an object and that is by selecting the outline. Outside of outline mode you can select an object's edge or if it has a fill, click anywhere inside the shape. This can make editing lots of layered objects a little annoying. Here are a few examples of how you would take advantage of this mode.
1. If you have lots of layered shapes, going into outline mode makes it easy to edit those shapes. If all of those shapes have solid fills selecting the right shape can be difficult in the regular mode. Outline mode is pretty much an X-ray view of your work.
2. This mode puts the focus on the shape. So if you are making a hand drawn font or working with scanned illustration, this mode allows you to see all of the vectors points making it easier to edit and clean up lines and vector points.
3. If you have a bunch of grouped objects and you need to adjust one of the shapes, you can go into outline mode, drag a selection with the white arrow tool around just that one shape or vector point and edit away. Then you don't have to ungroup and regroup all the shapes.
4. If you are working with another designer's files and notice a shape is cutting off for no reason, go into outline mode and you will probably see that there is a mask around that shape. This happens often when you open a PDF in Illustrator. Use the white arrow tool to select the corner of that box and hit delete twice to get rid of it.
There are lots of reasons to use this feature. Probably more than I know. I've been using it so long, that I dont even think about it, this mode is second nature when in Illustrator. Once you understand how it can be used, it will make your workflow better because the focus will be all about anchor points and outlines. If you are well aware of this feature, do you use it often? If you have some tips to add, sound off in the comments section.