The Giants have denied permission for the Falcons to talk to Steve Spagnuolo this week, meaning the Falcons can't discuss their head coaching vacancy until after the Giants' playoff run is over. Thus, there is no "courtesy" being extended by the Falcons; it's the Giants saying they don't want any distractions as they prepare for the Cowboys. And beyond, if they beat Dallas on Sunday.
The Falcons are also interested in Cowboys offensive coordinator Jason Garrett, who has already interviewed with the team during the bye week. Thus, the outcome of Sunday's game will be a major factor in the Falcons' search; whichever team loses will have one of its coaches freed up to further explore the Falcons' opening.
There is also no guarantee that Spagnuolo will interview with the team, especially if he doesn't feel ready to assume a head coaching position, or if the Giants' sweeten his current contract to keep him with the team.
The Giants are within their rights to deny permission at this point in the playoffs. According to league rules: "A team in the playoffs is under no obligation to grant permission for an assistant coach to interview for a head coaching position of another team. But if it does [grant permission], it must grant to all teams that inquire or none.
"Once its season is over, it cannot deny such permission through March 1. After March 1, it can deny permission (if the coach is under contract for the next season)."