As mentioned, compelling personas and a consistent voice based on your blog's vision help with branding. One of the big benefits of blogging is brand awareness. Consistency in the way that you present your brand through your blog, whether personal or professional, matters.

Your readers don't want to feel like they're reading a smorgasbord of content. They want to see some common threads that hold the variety together. A successful blog keeps content fresh with interesting personas while maintaining a certain style with a well-developed voice.

More importantly, you need personas and voice to connect with your audience. Always remember that you're writing for a very specific audience, not the whole world. You want to establish personas and a voice that appeal to that niche.

For example, Manpacks appeals to a predominantly male audience. The blog's personas range from comedic to inspirational. The voice, however, is always laid back and focused on "becoming a better man".