The division of left brain / right brain in marketing, sales and advertising is dead.
Clients no longer appreciate, nor respect, the inability of agencies to follow traditional business practices, and be beholden unto "the creative process" - which means the agency will deliver the goods when they're good and ready.
They expect process, accountability AND creative, all in one finely wrapped package. On time, and on strategy - strategy that sells, not strategy that looks pretty and people will remember for its "story." (What I call "voodoo creative" where the creative overwhelms the message.)
Clients are also demanding that their partners know more about what's going on in the entire world of marketing and communications than just what the agency, or agency management, sees through its limited prism. And excellent example of this can be found in this article:
I say this with confidence because my agency (www.sfamarketing.com) has recently won several pieces of business because we treat marketing as a discipline, and have been rewarded in kind.
Net net: the smarter you approach your client's business and satisfying their specific business-focused needs through defined, strategic processes, the better your creative output, and your overall relationship, will be.