And of course, there's this old chestnut: The ship travels at the speed of the plot.
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.")
I know Old Gene had only himself to blame for this; Trek was developing rubber rules about warp factor before the original series was even finished, because "the speed of drama" is a quicker, easier, more seductive path for the writer's room to take. But they really would have been better off taking Roddenberry's original scale and just sticking to it, and would have lost little by doing so.
[EDIT: Or, since sci-fi seems perpetually embarrassed at the prospect of taking its setting "too seriously" -- a bad habit that Roddenberry initially aspired to shake, but only ever very partially managed actually to get free of -- you can look at it from a different angle. If your ships move "at the speed of drama," how dramatically effective
is it really to present the appearance that distance is effectively meaningless in your setting and the Klingon homeworld looks to be a few hours' easy jaunt from Earth? Moving at the speed of drama, you still need some rough sense of speeds and distance that actually does heighten drama.]