You will certainly be provided with some "help" from the Marketing Department or the Communications Department if you do more than a few written or visual presentations. Remember that their intentions are generally good and that they have probably been sent from a senior manager. In many organizations, it is also part of standard practice.
On the other hand, remember that these people have been trained purely in the art of persuasion and, even worse, manipulation. That makes them poorly aligned with your goals as a duty-based, trusted advisor operating in an iterative decision-making context full of complexity and uncertainty.
Decorative visuals are added for aesthetic appeal and for humorous purposes. Decorative visuals are eye candy that usually interferes with learning processes. These visuals are a form of visual art; as such, they represent a one-way communication between the artist (from the marketing or communications department) and the data. Effective communication has everything to do with the receiver, not the sender, and therefore decorative visuals are poorly aligned with effective communication of issues with complexity and uncertainty. But one or two of these visuals can make the data more exciting and more appealing to some personality types.
Explanatory visuals, or information visuals, are meant only to show the important things in the data. These visuals are a two-way communication between the receiver (audience) and the data. Unlike decorative visuals, these visuals focus specifically on the central message of the data.
Keep it simple with two classes of visuals. Focus your attention on explanatory, or information, visuals that connect the receiver (audience) directly with the data and the important things that the data tells us. Use decorative visuals, or eye candy, usually created by the Marketing or Communications Department, only when you feel you have to do so. Reduce noise and trust your decision maker. Keep it simple.