Opacity has a lot of uses for different types of effects. We like to see certain things bleed through in some areas, while in others we want a shape or text to be a certain color. Recently, I was playing around with opacity in the appearance panel in Illustrator, and found a pretty practical use for it.
Some may argue that you can do the same thing in Photoshop, but I have found that you don’t get exactly the same results. For example, when we place a stroke around text, if the edges of the text are sharp or squared, then we want the stroke to follow the same contour. In Photoshop, is doesn’t always do that. You can align the stroke to the outside, the center, and the inside, which is handy, but they all tend to have undesired effects. Placing it on the inside squares out the edges, but is eats up and disfigures the shape of the typeface. On the inside, it doesn’t eat up your typeface as much, but it still changes the look of it, and on the outside, the corners become rounded if the stroke is large enough.
In Illustrator, you can bring the typeface to the top of the stacking order in the Appearance panel. This way, when you place the stroke, it doesn’t encroach on your typeface and change its look. Another great aspect is that you can apply multiple strokes from with the Appearance panel, and you can change the opacity as well. You can also select each stroke layer and apply an effect to it. This will let you have a multiple stroke object, and you could blur the bottom stroke, giving the last stroke a glow effect. You can also change the blending mode of each stroke, giving you a lot of flexibility with the look and capabilities of your objects in Illustrator. Basically, all of Photoshop’s filters are present, and you can apply them to any aspect of your Illustrator object. You can also do this to the main object or shape’s appearance.
One of the coolest things about this is that you can create a clean vector type treatment with opacity layers inside of Illustrator, and then you can copy and paste it into Photoshop as a smart object and it will retain the opacities that you had set in illustrator. Then, all you have to do is double-click your smart object layer and you will pop back into Illustrator and you can edit each individual appearance again. Save it and close it and go back to Photoshop to see the results.