Today, when warships are reworked, this gives them a specific new crew requirement that is the minimum
number of people needed to get the ship to do the tricks it's built or reworked for. No additional people are ever embarked because nobody wants to pay them.
But the Starfleet crews clearly include "idle" people, "passengers" who could and would be shoved overboard or pressed to useful duty in order to pare down the crew count to the absolute minimum if Starfleet were run by people of today. We never hear what the personnel requirement
of Kirk or Picard's starships would have been (except in "Remember Me" were various false figured are bandied about, sort of). We never hear what the personnel capacity
of these vessels would be, either. The only thing we ever hear is the personnel count
, and that is never indicated to reflect limitations or demands posed by the ship.
That aside, though, it is curious that the counts stay so consistent within a series. Picard's ship had people coming and going, yet there were two mentions of 1,014 people aboard; Kirk's ship likewise had various visitors, yet the figure of 430 was repeated. And Archer stuck to some 80 despite taking the MACOs aboard. An odd coincidence? A Starfleet regulation? Or indeed an indication of technological requirements or limitations posed by the ship's design, despite appearances?