There are a few things to consider, which would likely apply to both 23rd and 24th centuries equally...
In TOS "The Ultimate Computer", Mr. Spock tells us this upon sighting a "freighter":
M-5 has identified her, Captain. The Woden. Listed in Starfleet Registry as an old-style ore freighter converted to automation. No crew...
This indicates that automated interstellar vehicles are employed in the TOS era to convey needed raw materials (and perhaps other commodities and maybe even personnel). It also indicates that some such vehicles are manned, others are robots. (Later dialogue makes it clear such crafts could easily be manned, and that the use of the term "robot ship" makes it clear that the concept of the Woden being automated is not unusual, either.) It is not clear if the Woden is a Federation vessel, an Earth vessel, or even an allied vessel; all we know for certain is that she is that Starfleet keeps a record of her registry. We can infer from this that the Woden is either an automated Federation starship or that she is simply known to the Federation because she is employed by one of the Federation member-worlds. We do not know if her work has a military or a civilian purpose, but the casual way she is recognized by M-5 strongly suggests that such vessels (manned and automated) are widely employed and have been for many years. You can take this with a grain of salt, but this logic is being applied from canon material.
In TNG's "Unnatural Selection", the Enterpise-D encounters a call for help from the
U.S.S. Lantree, a Federation starship-of-the-line that is specifically identified as a supply vessel. (Another name for a "transport".)
This establishes clearly that
manned Federation starships-of-the-line are employed for transport/freight functions in the 24th century. This would seem to retroactively reinforce the notion in canon that Federation starships-of-the-line, both manned and automated, are employed for this purpose.
In July of 2008, I started a thread in the Trek Tech forum titled "
Warptugs and cargo pods", loosely based on the TOS sighting of the Woden and Franz Joseph Schnaubelt's notion of a Class I Transport/Tug Starship from his 1975 Star Fleet Technical Manual. The thread included discussion, art and model exhibition of what military (and civilian) transport vessels carrying cargo pods might look like and how they would be used. In was all very loosely derived from canon, but can be traced back to mentions of the Astral Queen, the Woden, the Lantree, and other instances.
It is my belief (and my speculation) that the TREK Universe had a vast, mostly unseen network of frieghter/transport/"supply ship" vessels, some Starfleet starships-of-the-line, mostly not, some manned, most robotic. Some were self-contained vessels like the Lantree. Others would be warptugs piggybacking cargo containers. The collection of these vessels formed a kind of interstellar railroad/pony express/FedEx/Post Office between the various trading worlds, colonies, space stations, starships and starbases. While this speculation itself isn't canon, it is strongly inferred from numerous references sprinkled throughout the franchise.
Some folks had a hard time buying into my idea that this "freighter" infrastructure existed prior to TOS, but it is the only way I could figure out how the human race became networked with other worlds prior to the Warp 2 threshold being crossed by the NX Project prototypes.
As far as I'm concerned, these "interstellar railroad" vessels were being employed prior to ENT and well after TNG. We just never saw this network explicitly in action.