The immediate reaction from most people is to yell out in frustration and quickly find a way to turn the feature off. After all, nothing is more annoying than paths and anchors highlighting all over the screen as you move your mouse around. And in all honesty, I agree -- Smart Guides in this way is totally annoying -- I too would turn it off. While I could probably find some benefit to having the boundaries of paths light up, I can find even less reasons for having Illustrator identify objects as "paths" or "anchors" -- first of all, I like to think I'm smart enough to figure that out on my own, and second, what can I DO with that info? When would there EVER be a reason for why I'd need to have something identified as a path or an anchor?
OK, so most people run to the View menu and choose Smart Guides -- which effectively disables the Smart Guides feature in Illustrator. Here's where I offer my plea: Don't turn off Smart Guides. There are just too many important benefits to the feature, and by turning it off, you are doing yourself a disservice, especially so in Illustrator CS4. Let me explain.
Have you ever tried snapping an object to a guide or another object, thinking those objects were perfectly aligned? Only to zoom in really close and see that there's actually a gap? Of course you have. A common misconception about Illustrator is that you have to zoom in REALLY really close in order to make sure that object line up correctly, and that this is a cause of Illustrator not being accurate enough. In reality, it's due to the fact that the snapping behavior in Illustrator is calculated from the position of the CURSOR, not the object you're moving. That means if you click on a particular anchor point and move your object to snap to a guide, you might THINK that you're snapping the point to the guide, but you're really snapping the position of your cursor to the guide. In other words, if you don't click directly on the anchor point, your anchor point won't end up being aligned perfectly to the guide.
That changes in Illustrator CS4 -- IF -- Smart Guides is turned on. When Smart Guides is on, Illustrator can snap the object bounds of objects to paths and guides (the way InDesign does). In other words, with Smart Guides on, your objects will snap, and you won't have to worry about exactly where you click to move an object from, and you won't need to zoom in really really really close to ensure your objects are aligned correctly. That's a pretty big benefit, don't you think? Then add the additional benefits of Smart Guides -- quickly aligning objects as you move them around. You'll find yourself using the Align tools a lot less. And you'll find yourself zipping around your work, and being more productive.
But what about all the highlighting and stuff? Well, Smart Guides is actually a complex feature that encompasses six different TYPES of guides. In my book (shameless plug -- it's coming out December 18!), I detail each of these six guides. But here, I'll tell you which guides I use and find to be important.
Illustrator has a preferences panel specifically for Smart Guides.
The Smart Guides behind the flashing and the highlighting are Object Highlighting and Anchor/Path Labels. Turn those off for a heaping dose of peace of mind. TURN ON ALIGNMENT GUIDES -- this setting allows you to easily align objects as you move them around the screen, and more importantly, it activates the snapping behavior I mentioned above. As an added benefit, Alignment Guides also work on Artboards when you're in Artboard Edit mode. Finally, as an added suggestion, I personally like the Measurement Labels setting -- this displays values as you move, draw, and transform objects.
So instead of turning off Smart Guides, learn to control them -- make them do only what you want them to do. In the end, you get a better Illustrator experience overall.*
*Go ahead, I know you've got a burning question: why did Adobe turn on the Object Highlighting and Anchor/Path Labels setting in Smart Guides? Did they really think people would find it helpful? I don't have a good answer. Maybe it was so that I would be able to write this blog post :)