I have always thought that Will & Grace was basically a farce, with unusual plotlines and witty one-liners. In this live show the actors are limited to one set. As such it looks like a stage farce (including the constantly walking in and out of doors). The writers were forced to write longer scenes, which greatly benefits the show. (One of the irritating elements of the post-Seinfeld sitcoms is this habit of writing incredibly short scenes.)
The actors seem to enjoy the experience as well. Miss Messing has some trouble keeping a straight face, but no-one makes the mistake of playing too much to the audience.
In a weak season this episode stands out even more.