In a quote from Total War Medieval II - "He who defends everything, defends nothing".
But its somewhat true today. There iare not lone cruisers or destroyers guarding merchant ships or sitting off the big ports. The mostly group together in fleets that can handle whatever the leaders think will be sent against them - except for subs of course.
Mike S.
Well, fleets are still dispersed throughout their area of operations, for the most part, although you are right that generally you won't see a carrier running alone. And the situation isn't really the same. In today's world a ship can get anywhere in a week or two, and planes can get there in hours, no matter where you are going. And, of course, communications are light speed, which means that in many cases you can have real-time communications in between theater command centers and any junior officer assigned to that command center, no matter where they are.
In a large Starfire empire it will take months, maybe even more than a year, to cross an empire even at cruiser speeds, and communications, even with an ICN in place, might take days or weeks. What government could resist pressure from a major population center for local defense units when that population center is, say, four months travel time from the nearest fleet base? Or even one month?
Kurt