The best kinds of marketing campaigns are those that aim for a goal or end result, and are made by people who have a vision and expectation of what they want. Mediocre marketing campaigns that follow the norm sometimes get lost and don't end where people may like.
Brand visibility
If you are starting up a brand, or just hopped on board working for a brand, chances are you are or will become quite passionate about it. I mean, it's what you will be working with for at least 30 hours a week, right? Working closely to create a marketing campaign for a brand will allow you to find an audience that appreciates your work and finds it useful. This also leads to referrals and recommendations from existing clients to new prospects! Sounds like a win-win situation.
Positions you as an expert
Once you have successfully pulled off a rockin' marketing campaign, other people in your industry will start to look up to you. Isn't most of our goals to gain credibility and authority within our industry? If people don't trust your work and take it seriously, then what is the point of spending so much time on it in the first place? Ways to work on this include speaking at an event, consistently writing a blog, and teaching a class or workshop relevant to your field.
Happy and loyal clients
Networking, networking, networking. Something we all have to do when looking for our next clients. Sometimes it is successful, sometimes it is not. Proving to your customer that you are capable of creating and executing an awesome marketing campaign will have them coming (and staying) back for more. Seeing the happiness and satisfaction on your clients face when it's all said and done is what brought you here, right? :-)