One reason to practice is to approximate the discomfort of the real thing.
Doesn’t sound fun, does it?
Athletes train in order to build their speed, skill, and strength, but also to get familiar with what it feels like to be deeply uncomfortable. Knowing that the 800 meter dash creates a specific sensation is valuable information for the runner, and they need to know what it feels like before they get to the big race.
When we practice a presentation or a talk, we may feel silly or self-conscious. That’s good! If we don’t have the experience of nervousness or self-consciousness when we practice, we might be unpleasantly surprised by it when we show up for the real thing.
Discomfort is the primary reason we don’t practice, and it’s the primary reason we should.