That's an idea for some situations. Basically ground crew, like aircraft use. Definitely something that would apply for an interplanetary ship that's only taking short periods between landings (a Moon shuttle would be a good example, even a really big one).
Either the shipping line employs its own, or you can hire staff at an appropriate starport - I'd say class A through C, although there may be capacity limits on public facilities. Best to book ahead of time.
Bridge crew, service crew and gunners clearly have to be taken normally - they have outside of port duties. Some maintenance crew and engineering will need to be on board - unlike a fighter jet or airliner which are aloft for a day or two at most, Traveller starships are away from port for over a week. You need at least one Engineer to be on board to make jump.
I'm thinking that maybe you could get away with being able to shift half of your rated Engineering and Maintenance requirements (dropping all fractions) to portside crew. Same pay grade, but you don't have to cover their life support or provide accommodation. Note that this will not affect most player ships (400 tons or less) as they usually only have 1 Engineer and no Maintenance position anyway. The Subsidised Liner could shift one of its three engineers to portside, I guess. Or two of them if you go with another way of calculating it.
On the other hand, if it turns out that not enough are available at the port after all, you'll end up being unable to meet maintenance requirements for the ship for a maintenance period. Which is not ideal.
Robot crew may be a better way to reduce life support and accommodation costs.
Military craft should carry their rated crew, though.