Generally, branding guidelines are a good idea. They provide consistency for both the appearance of a brand (logo colors, for example) and where or how it is used (putting the brand on coffee mugs but not on shot glasses, perhaps). But Ron E., posting at brandcurve.com offers "3 Reasons why 'Branding Manuals' are bad for your brand." He's not really saying don't have one, just identifying some of the potential problems. As a designer you may or may not have much input into a client's branding manual, but understanding it and some of its weaknesses could be useful when discussing your concepts with clients.

