All imagery and collateral should have a consistent look and feel. This doesn’t mean you need to use the same image and layouts over and over again, but you should have a well defined visual style.
A logo is a piece of a much larger puzzle called ‘branding’. Yes, a very large piece of the puzzle, but your logo is by no means your brand.
In a nutshell - to make it a breeze for you, so you can spend less time worrying about the technical stuff and more time growing your business.