I have preached repeatedly on the importance of a consistent look and message across all touchpoints, all advertising and marketing items.
Also that all branding elements (brand identity) should come from the same place and communicate the same sense of who you are. That there should be a coherence and authenticity to how you look and speak.
If this is done well, repetition over time then builds priceless brand recognition that greatly multiplies the effectiveness of all your marketing efforts.
Seth Godin has pointed out another reason for this kind of consistency. "You only get once chance to make a first impression" is a truism but what is rarely recognized, you don't know WHAT is going to make that first impression.
People don't notice your advertisement the first time it runs. Maybe not the tenth. And then what is the first thing they notice about it? You have no way of knowing whether it will be your tagline, logo, color scheme or the tone of voice of the announcer.
And maybe it is none of those. Maybe it is one of your delivery trucks or the sign on your warehouse or the main graphic on the home page of your website....