IKEA is known for selling plain, almost stark furniture for a reasonable price. Many people use it as-is, since the utilitarian look is a legitimate design choice, but others view it less as an ending point and more of a blank slate. With additions such as stencils, overlays, trim and other tools, you can dress up furniture into something that really shows your personality.
Customizing your furniture allows you to create a custom standout piece, but it does more than that. It turns an item into a one of a kind piece of furniture that your friends might be jealous of and allows you to manipulate your furniture to get it to fit into your home's theme and style. So, instead of searching forever for that perfect complementary end table, you can just make it!
Overlays come in a huge array of styles and sizes to match with almost any imaginable aesthetic and you can paint them any color you like. Try contrasting or complementary colors, a muted echo of the shade used on the underlying piece, or bright combinations to achieve the look you are going for.
In all cases, the overlay elevates the furniture from something flat, boring, and rather bland to something with a little more zing. It can be a great way to create Victorian and vintage-style pieces without having to pay the cost of reproduction and antique furniture, to dress up your furniture for a mod or glam look, or to just have some fun when it comes to how your furniture looks.
You can also use stencils to great effect when it comes to changing the look and feel of furniture, as well as applying specialty papers. Can't find a paper or applique that suits your purposes? Check a fine paper store! They often have amazing paper (at very reasonable prices) that you can totally apply to furniture -- you'll just need to seal it to protect it from hard use.
Don't be afraid to hit the hardware or lumber supply store for basic trim and beadboard as well. Adding them can totally change the look of a piece of furniture by eliminating harsh angles and creating smooth transitions.