Sigma's E45 small tapered blending brush is of course for blending. What makes this brush a little different from alot of other tapered blending brushes is it's pointy tip, making crease-work easier. It's pointy little tip allows you to get into those little spots with more precision. It's fluffiness still allows you to blend effortlessly.
Most likely, you've heard that the Sigma E45 is a dupe for MAC's 226 brush. The two things that make this brush better are of course the price but also the tips are different. As a makeup artist, I want the best quality for the lowest price for my pro kit. The Sigma E45 also has a pointy tip whereas the MAC 226 is a bit rounded at the tip. I'd prefer the Sigma E45 for a tapered blending brush on myself because of my small eyes.
Do you use a tapered blending brush? If so, which one do you like to use?