There are three possibilities that I can see.
The first is if less than half of a baseball game (four and a half innings) is played, then the game is canceled and a completely new make up game is scheduled. That, I can follow.
My understanding is that if the home team is leading when the game is interrupted during the bottom of the fifth or later, the rest of the game isn't played, and the home team gets the win.
There was one instance I remember, when the rain interrupted the Yankees, who were leading 2-1 in the top of the 8th . There was a partial "makeup" on a subsequent day, not of the whole game, but of the remainder of the eighth and ninth innings.
Then there's the case of the Pirates at Atlanta tonight, with the visitors leading 3-2 at the end of six. I read that unless the game were continued the same night, a victory would be recorded for the Pirates over the six inning game.
If the home team is leading after four and a half, determination of the win seems trivial. But if the visiting team is leading, how would they determine whether the game will be scored as a visitors' win or continued later from the point of interruption?