Using disabled states for buttons, links and other ui components are an important way to provide feedback to the user. Think about a stop light for a minute; if it were always green then the driver would expect that they could drive through causing collisions with cars going the other way. To prevent this, the red light steps in to tell the driver they have to wait. Just like stoplights allow traffic to run more smoothly, the disabled state allow UI interactions to be more efficient—the user knows that they don’t need to waste their time trying to click anything disabled. In addition, it helps hierarchy because applicable actions stand out whereas unapplicable actions push back. Disabling an action communicates important information to the user which, coupled with their interaction with the product, help them to understand how that product works.

For example, when the link button is disabled (shown, below), I infer I have to do something to allow that button to become active: I have to highlight the text before I am allowed to add the link not click the link button and then tell it what text to insert for the link.

Other Examples:

I think disabling components is a must! Vote ‘em up!