What Rambler was referring to was the distinction in the Star Fleet Universe between Tactical Warp and non-Tactical Warp; and it is a key one.
Non-Tactical Warp is the use of fusion-based impulse engines to propel a ship at trans-light speeds strategically (at a rate of nine parsecs a day), but only at sub-light speeds in combat. (Well, there is still a sort of warp bubble around the ship, in order to allow it to side-step problems with time dilation and Newtonian motion.) Fusion-armed ships rarely have shields, rely on armour, and have lasers, atomic missiles, and other such weapons.
Tactical Warp drive is antimatter-based, and allows a ship to travel far faster at a strategic level; but it also provides a warp bubble sturdy enough to allow a ship to fight at low warp speeds. Also, tactical warp allows a ship to be equipped with other toys, too; such as phasers, photon torpedoes, transporter beams etc.
In game terms, it's worth noting that in
SFB, each hex on the map is 10,000 kilometres across; Earth would fit snugly into a single hex, for example. A ship moving at impulse can only move one hex a turn; a tactical warp-powered ship as many as 31 (30 from its warp engines, plus the one for its own impulse drive).
It also means that, in technological mismatches, the older ship is in a lot of trouble. An old ship needs a sensor upgrade to even detect ships and weapons moving at tactical warp speeds in combat; when the Klingons and Kzintis first developed warp-speed drones and started using them against each other, they seemed to impact before their own sensors could detect the impact. Even with a new sensor suite, older weapons which were mainstays in the sublight era suddenly find themselves short-changed in terms of range and hitting power.
This was shown in stark detail in the
Early Years, at the point just before the Tholians arrived in our galaxy. The Klingons were expanding to the south of the Federation (who they hadn't met just yet) when they ran into the western edge of the Romulan Star Empire (which was attempting to expand around the Neutral Zone agreed with the Feds decades before). At this time, the Klingons had developed their first tactical warp-powered starships, while the Romulans had not.
Klingon ships, two generations removed from the ones you'll see in
A Call to Arms: Star Fleet, were still able to literally dance around Romulan ships; in one battle, they smashed an entire fleet defending a Romulan base, which they then looted and demolished in turn. The bottles of Romulan Ale captured in these raids became prized trophies in the Deep Space Fleet; the Romulan navy did not even know what had happened to their lost ships and bases.
Only the arrival of the Tholians, who happened to land right in the midst of the space the Klingons were establishing as a launchpad for a full-scale invasion of Romulan space, stopped the Klingon trefoil from being flown over Romulus and Remus.
(Even after the treaty which saw the Klingons provide tactical warp to the Romulans, the latter didn't uncover the truth about what might have been until well into the General War.)
So, in short, a ship travelling at sublight, with weapons unable to target (let alone damage) ships and seeking weapons travelling at warp, will likely find modern-era Star Fleet Universe ships to be more than they can handle.