Have you ever tried to create a smooth selection using the Lasso tool? It’s just about impossible, right? (If it sounds like it isn’t, give it a try—open a new document, take the Lasso tool, and draw any random selection, and then look at the selection. It’s jaggy—not crazy jaggy, but it’s certainly not smooth.) If you were trying to create a selection for an interface design, or a realistic element of some sort, it would just be too jaggy to use. Here’s a tip:
(1) Press L to get the Lasso tool and draw around the area you want to use as your selection.
(2) Press the letter Q to enter Quick Mask mode (your selection will now be surrounded with a reddish hue).
(3) Go under the Filter menu, under Noise, and choose Median. As you move the Radius slider to the right, you’ll see your edges smooth out.
(4) When it looks nice and smooth, click OK then press the letter Q again to return to Standard mode, and you’ll have nothing but a nice rounded selection.