i use a wider binding for thicker quilts (like flannel quilts i usually use 2 1/2" or even 2 3/4"--depending on how lofty the batting is-
i prefer narrow(er) bindings on other quilts- and sometimes even use 2"- it does depend on what you like- and the project itself. i tend to use 2 1/4" most of the time- and once even as narrow as 1 3/4" or 1 1/2" for small projects like doll quilts- or table runners. i like facings too- if i really don't want a binding to show....it's all dependant on what you like- and the project you are working on- what looks best to you- a binding can be wide and part of the overall design-if that works for the project.