I recently re-watched TNG's sixth-year ep "Schisms", then looked it up on Memory Alpha. This odd quote, under the Continuity section, humped out at me: That quote leapt out at me because I misinterpreted it at first. In TOS, when someone has the conn, they are left in command of the Bridge itself, not just the helm. Of course, it would be unusual for the ship's first officer to take the helm. (Which is what the quote was supposedly about.) Riker was apparently in command of the ship while Picard was sleeping in the teaser to "Conspiracy". Picard is seen directly leaving Riker in command so Picard can beam down to Starfleet Command HQ on Earth in "Conspiracy" as well, and also so Picard can lead an Away Team to the surface of Iconia in "Contagion". Has anyone kept track of the times Riker was in command of the bridge, throughout the TNG TV series? There are other comments about this ep, quoted from the producers. Apparently, everyone regards the episode as a dud. I agree there were problems with it, but they seem to focus on the wrong issues. The aliens look weird enough. But the biggest problem is that in the end we have no idea what the aliens are after. The aliens attacked the Enterprise, one person at a time (excluding their weird wormhole thingy), and in the end we have no idea why. That's by far what stood out to me. But the people behind the show fretted because the aliens looked like "monks". So did Emperor Palpatine, but that didn't stop him from being a menace. Actually, of all the alien invasion attempts in TNG, this one stands out as being the most interesting and having the most unrealized potential.
IIRC, what TOS called "Helm" and "Navigation", TNG called "Conn" and "Ops". Although strictly speaking it seems like Ops is something entirely different, and Conn is actually some kind of combined Helm/Navigation console. TOS was more likelie to use the phrase Conn to mean overall command of the bridge.
Most likely as a reference to the fact that when a person took control of the tiller or ship's wheel they had control over the direction the vessel took, and were in a sense "in command", particularly during tight battle maneuvers. TOS liked to throw out a few sailing references from time to time.
"Conn" in TNG is short for "flight control," which is the combined helm and navigation function on a Galaxy-class starship. The Memory Alpha quote is saying this is the only time Riker mans this station on the bridge. In TOS, "you have the conn" was parlance for "you are in command until I return." In TNG, that morphed into "you have the bridge."