The key is that each presentation aid must directly express an idea in your speech. Moreover, presentation aids must be used at the time when you are presenting the specific ideas related to the aid.

When Should presentation aids be used?

Presentation aids can fulfill several functions: they can serve to improve your audience's understanding of the information you are conveying, enhance audience memory and retention of the message, add variety and interest to your speech, and enhance your credibility as a speaker.

Why might you decide to use presentational aids in your speech?

When your graphic images deliver information effectively and when your listeners understand them clearly, audience members are likely to remember your message long after your speech is over. An added plus of using presentation aids is that they can boost your retention and memory while you are speaking.