Body language is important when presenting to an audience. You must perform confidence. This can be achieved by being mindful of your posture, stand up straight, and make eye-contact. You must project your voice so the whole room can hear you.
This is important because you want to engage with your audience. If an audience is engaged, they’re more likely to be listening to what you're saying. It’s important to use a range of tools to keep your presentation interesting. Humour should be used (somewhat sparingly) to keep the tone light, and images and quotes to keep audiences engaged. Keep the text to a minimum and speak succinctly.
In the context of presenting a pitch to investors, the goal of keeping your audience engaged is the no.1 priority. If a pitch does not appeal to investors they will not want to invest in you. Similarly, if your idea is amazing, but your presenting skills are lack-lustre, or if your pitch is longwinded and boring- you will not receive investment.