“Wait a minute! Did I leave anything behind?”
Rabbi Yehudah HaChassid writes in his tzavaah (living will) that a person who sets out on a journey should not return home to get something he left behind. Instead, someone else should go into the house to retrieve the object for them.
What is departure?
This restriction applies only if one has already left the house, not if they are on their way out and wish to go back into a room they have left. Some poskim say that even if the person is already outside, but has not yet bid goodbye, they may return.
Avoiding return only applies to the day of departure, not to the following day. Someone who left home but then cancelled their plans to travel, may also return home. There are poskim who extend this consideration to someone whose journey is delayed for a set time—and permit them to go home to wait it out.
There is an argument among poskim whether the intended purpose of return is taken into account; some aver that going back for a dvar mitzvah (an article used for a mitzvah) is permitted.
What about stopovers?
There is a difference of opinion among poskim whether this restriction includes a traveler already en route with multiple stopovers, and they have left one midway location for another: May they return to an earlier stop in their journey? Some poskim consider it the same as leaving the starting point, while others maintain that returning to a place mid-journey is permitted.
Delayed Flight FYI
It has been related that the Lubavitcher Rebbe recommended the following to a person whose flight has been delayed and was in a quandary whether he was permitted to return home: “Study a chapter of Tanya”, i.e. take some time to contemplate the greatness of the Creator and reach new heights in avodas Hashem (service of G-d). As a “new person,” you may go back home.