Strong brands are really all about constraint. The role of marketing and communications is to find the edges of a brand and create within those limitations. As soon as a brand starts relaxing their constraints, it will be the brand that becomes weaker.
Indeed, there are countless examples of how constraints – seemingly confounding as they were confining – have resulted in brilliant creative solutions. Without constraints in language and messaging, budget, time, etc., brands tend to become too “full of themselves.” They go a little nuts with big production values, big celebrity endorsements and things that are less and less essential to the brand. In doing so, they wind up "talking to themselves." They shoot themselves in the foot and become more and more forgettable.
Sarah Shearman’s Campaign post is definitely worth a look.