And a less sophisticated way; If you're just zooming to reframe your shot you doing videography, not cinematography....I was merely meaning that using a prime lens requires a certain type of situation where as a zoom lens allows you to frame a shot in a more flexible way...
Maybe you just mean you don't have to swap lenses?
But each focal length affects many things about the image such as the relative distance from one object or actor to another object or actor. Cinematography is about making decisions like that. Maybe the characters should seem distant from one another, maybe they should seem very close. If you're just zooming in without moving the sticks to change the frame without considering not only the frame but the spatial relationships and DOF that's right for the story telling then you're not telling the story visually.
Now you can do that with a zoom lens - pick focal lengths and apertures that help tell the story in conjunction with moving the sticks for the framing - but it sounds like you just wan to zoom in for your closeup like soooooo many people do when shooting bare lens with a video camera.
With a DSLR changing lenses takes only a little longer than taking the lens cap off and on the HMC 150.