Large chains (mostly) know the value of a consistent image. Loyal customers expect their dining experience in Houston to be the same as it was in Chicago. Loyal buyers of a clothing brand learn to expect a certain quality and look from any new purchase. Consistency in packaging and communications simply reinforces that expectation. A different logo or look throws up red flags that something's new and suddenly, even if the product hasn't changed, the perception is influenced by the expectation.
I ran across 2 brands that must have very different methods for maintaining their image. The first is Maggiano's Little Italy. The image below is a screen grab of a simple google image search. This search was actually the impetus for this post. Maybe there's more to this story than I realize but this brand is simply not helping their image with loose or missing graphic standards.
Contrast the same exercise done with the Pei Wei logo:
Pei Wei has different versions of logos for different uses but the overall look, the typeface and the mark are noticeably consistent. Even a search for just "Pei Wei" shows their attention to color as part of their brand. Look at the grouping below, pulled straight from Google image search. Red floors, red plates, red menus. What a great color cast to reenforce the spicy tastes and the hot woks used to prepare the food.
The takeaway is to take the time to put together a solid set of guidelines that can be distributed to your designers and creative vendors. Consistency goes a long way in reassuring loyal customers that your business is here to stay and your product will continue to please.