Many people, when they first begin recording and producing sound assume that if you get a nice microphone and camera, you can produce great dialogue sound straight out of the camera, no need for post production.
I haven't generally found that to be the case.
Without getting into arguments over what kind of gear you need, there's the reality that when you record, you need to leave headroom when setting your levels. But then when you're done recording, your dialogue isn't all that loud.
I typically use clip gain and compression to even out my dialogue audio clips. Once I've got it all leveled out, then I loudness normalize the dialogue. Then my audience isn't straining to hear the quieter parts or riding their volume control to hear everything.
Psychologically, louder sound also sounds better (a complicated topic that I hope to understand better some day). I don't mean audio that's so loud that its all crushed and distorted, of course, just, clear, present sound.