For my money, a lazy writing habit that became part of what stultified the original Trek style. The "speed of drama" conceit means you can never tell convincing stories in your setting in which you can derive drama from a sense of place and distance: for example, it effectively closes off the kind of drama we see in The Hunt for Red October, where everybody is working against a clock that consists of the Red October's travel time from Poliarny Inlet to within launch distance of America's eastern seaboard. (I mean, you can still attempt stories like this, it's just a lot harder to really sell them in a setting where everything is next to everything and ships "move at the speed of drama.")
The film The Hunt for Red October
has more than its fair share of errors, when it comes to the positions and velocities of the various subs throughout the film.