There is a natural tendency to exploit the direct relationship to click-thru-rate and the size of the visible clickable area.
This law was noted before the "interweb", in late 1989, when online service providers first started having interfaces that allowed navigation via a mouse and tracking the relative success of triggering that navigation and stake holders has metrics they were measured on. Though it may seem like an intuitive law since its a natural behavioral extension of Fitt's Law. The tendency to exploit this relationship continues even today, especially, if you rightly consider a tap a click. And Fitt's Law is definitively true in both extremes. On the high end, if all your display is taken up by a single clickable element, then given no other option then that area is very likely to be clicked upon. In this extreme it is the mouse version of the keyboard's "Press any key to continue": "Click anywhere to continue." On the low end, if your clickable area is a 1 by 1 pixel, it will have a very extremely low click-thru-rate. In that model, clicking on it is more like trying to find Waldo in the crowd.
CTR or click-thru-rate is simply the number of times a unit is clicked divided by the number of times that unit is displayed. This is typically expressed as a percentage (%).
Often the success of a online product or initiative is based on achieving or improving CTR. And sometimes that might even translate into someone getting compensated based on the level of that success. That is the crux of The Law of Clickable Space: there may be potentially nefarious forces at work on your product:
But these often aren't indications of success, but rather an indication of failure or abuse.
Larger clickable units, often perform better, but for the wrong reasons.
A larger clickable unit may take undo attention away from the natural flow and experience for the user and force them into a path that they may not have naturally pursued. In essence, you can herd clicks. The larger the unit is, the more likely it is to herd.
A larger clickable unit does result in an increase in accidental clicks. Users accidentally or purposely click on areas in a web browser. A user may simply have been trying to put a browser in focus, or attempting to access a scroll bar, menu, or otherwise interact with the page and hit the clickable area of a given unit. The larger the unit, as well as the closer it is to interactive elements (part of The Law of Incidental Clicks), the more likely you are to have accidental clicks.
Smaller clickable units, often result in positive results also for the wrong reason.
A smaller clickable unit does result in a decrease in accidental clicks. Users often are unable to locate a link that they want to use. The prime example of this is the micro text in present in some newsletters to unsubscribe from them. The link is small obviously because its an action that the newsletter sender does not want you to both find and take.
Good units don't "game" users: they should be clear enough and specific enough to allow the user to intentionally and not accidentally click on it. Product developers and managers need to develop guidelines and standards on this. But there are natural dynamics that may cloud our judgment, or different opinions on what is clear, and the combination of that may result in gray areas.
To augment standards good product methodologies will attempt to gage how intentional given clicks really were as well as if users can't find the links they want to use.