Why have brand guidelines? Starbucks.

Starbucks Thumbnail incorrect aspect stretchMix999 FM in Toronto is running a flash hero in the center of their landing page, and I'd bet dollars to donuts that Starbucks did not approve the artwork. How do I know? No billion dollar brand would allow their logo to be stretched to fit a space. Aspect ratio is important, and keeping it consistent is fundamental.

I see the same sort of laziness when big events have to make banners and fit 25 sponsors' logos in a big blob at the bottom. They take low-res raster images off the web, sometime with a black background destined for a white banner, and don't bother to scale properly, seek approvals, seek proper vectors, scale, or like many brands require, observe white-space or 'protection-space' restrictions. (logo must be x % away from nearest border or other element, and must be x % scaled to space, etc). Big brands spend big bucks on this work from their creative agency partners for a reason. It's all about consistent messaging and impressions of the brand.

For a recent example, take a look at Bell's brand site. You can even download the logo along with the guide on how to use it.