To write effective marketing campaigns, campaigns that really connect with people and drive them to action, a copywriter needs to understand your business, your marketing goals and your target market. They need to understand the values your business holds dear and what makes you unique.
All of this information forms the foundations of your business branding but not everyone has the answers at the tip of their tongue. You might have a grasp on the generalities of your branding but the devil is in the details, and really effective copywriting needs those details.
This is where good copywriters really come into their own, helping you realise the branding foundations you need to make your marketing really effective.