No matter how good the dialogue might be on a TV show, viewers will change the channel if all they see are two people sitting and talking to each other. That's why TV characters are almost always doing some kind of business while chatting, whether it's folding laundry or getting dressed or even just walking.
In fact, the "walk and talk" is one of the more common scenes viewers will see on TV today. Usually taking the form of a long, uninterrupted shot, two or more characters talk while walking down a series of hallways. The technique became well-known for its use on shows created by Aaron Sorkin like "Sports Night" and the more successful "The West Wing."
As a cinematic technique, the walk and talk increases tension in a given scene, showcasing just how busy the the characters are. It also works great as a transition scene, moving the action from one location to another.
It can also be a tool used for comedic purposes, like in the "West Wing" episode that flashes back to the origin of the walk and talk meeting (they came about, in part, because Sam and Josh couldn't find the room they were supposed to meet in). Or, in the "House" episode "Ugly," Dr. House makes a self-referential comment about the walk and talk, saying "Let's go for a walk. Walking gives the illusion of the story moving forward."
Another show that's chock full of walk and talks (many of them very funny) is USA's legal drama "Suits." The term gets a shout out in the episode "The Shelf Life," while the pilot episode alone has at least 10 instances. Most of the time, the walk and talks are between Harvey and Mike, and include plenty of quips and pop culture references.
"ER" also had frequent walk and talk scenes, which makes sense for a show set in a high tension, fast-paced work environment. But there's another reason, too: The director of photography for "ER" was Thomas Del Ruth, who later went on to work on the pilot of "The West Wing" and is partially responsible for the show's distinctive look.
But TV shows beware: too much walk and talk is never a good thing. For example, Television Without Pity famously lambasted "CSI" for an overabundance of these types of scenes, with one writer famously quipping that the hallways of the lab should be called the "Labitrail," a take on the Habitrail-style mazes that pet rats often play in.