This is a new feature in SharePoint 2013 to control routing and throttling of your SharePoint. Thing you can do is to check the incoming url, specify your rules on how to handle the request. Unlikely Throttling in SharePoint 2010, where you can only specify what is the maximum number of list item to be displayed (For example)
Another example is to deny requests from agent with “Microsoft Office OneNOte 2010”. Additionally, you can specify the expiration of rule or to use a health score threshold to activate it. (Interesting…)
Routing Weights (aka Load Balancing) is a form of control to servicing WFEs. More powerful WFE can be associated with lower static weight (0 being the lowest) and therefore will get the most requests. Another weight which is health weight is updated by Policy Engine (SharePoint). This weight can be used for routing rules as well.