A word is a visual aid, because a word is a symbol for that which it represents.
Sometimes many words are needed to communicate ideas and concepts.
When you reach the stage where many complex ideas are being presented in your document, one of the choices you may need to make is to find a visual aid that can tell the story of what you are trying to say faster through a visual image.
Choose that image or visual aid in the same way that you approach constructing any type of document: use your deductive brain to select the image that tells the most the fastest.
Think about your resume. It is a visual aid. It tells the story of you work and education history fast, telegraphing key ideas quickly using words. But the whole page (or pages) of words is a visual aid.
Most documents have the capacity to be seen as a visual aid, but there will be all kinds of flexible occasions when you will select from a growing assortment of possible images that include charts, graphs, photos and video clips.
You may even use clip art.
There's nothing wrong with clip art if you you choose it because it fits the purpose and occasion of your document and won't offend or repel your document.
The most obvious problems with clip art is that there is a clip-art feel to the elements. That may not matter to you. What should matter is that you don't take the first piece of clip art that is vaguely associated with the idea you want to telegraph. The visual aid tells a story. The right visual aid tells the story you want to transmit. The wrong--or not exactly right-visual aid will have an undesirable effect of confusing your reader.
Beware of sending mixed messages through your visual aids.
Be especially careful of tone. You don't want to mix and match real photos with cartoon characters, and you certainly don't want to use cartoon figures for an occasion that is more serious than that.
Remember too that the artwork or visual aid that you select may show up on a piece of paper, on a computer screen or be displayed on a very large screen if it is part of a PowerPoint presentation that is projected so a crowd can see.
In short, visual aids are powerful tools to help workplace document creators tell the stories of business.
Just remember, it's not about decorating or playing with bells and whistles; it's about telling the the truth of what you need to share. Keep that serious ambition in mind, and your selections of visual aids should fulfill the purpose, attract the reader, support the tone of the occasion and fit the environment of the reader.