You can find convex curves in lost of places. Scallop edges on a quilt, maybe a round pocket or ears on a softie. To make the curve nice and smooth it is important to clip around the curve.
The example on the left is left as is but on the right I have used my pinking shears to clip the curve along the seam. You don't have to use pinking shears, you can easily snip little triangles with normal fabric scissors. Or maybe a pair of small sharp scissors. And you don't always have to do as many snips, or as close together as here. But snip, snip, snip you must!
And this is why: on the left the curve is sort of smooth, but it's more like a series of small straight edges that form the curve. Because once the curve is turned right sides out, the fabric along the seam is bunched together in a smaller space than before turning, and that creates these 'segments'. It doesn't look great. In some cases you can get away with not snipping along the curve, but it is a habit worth having.
Because look at the example on the right. What a nice smooth curve! (The circle isn't perfectly circular, but that's not the snipping's fault. The sewing machine operator is to blame.. ;-) )
You don't have to make as many snips as the pinking shears will do, but you will need to cut away approximately 1/3 of the seam allowance, preferably more if you have the time/can be bothered. :-)
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