Evidently the disciples (v. 22) wanted to know where this judgment would occur. Rather than giving them a geographical site, Jesus told them what to look for. The presence of corruption would indicate the coming of one to clean it up. Similarly the presence of a dead body outdoors indicated that a vulture would be along soon to eat the carrion (cf. Matt. 24:28).
"Vultures hovering over dead bodies graphically depict the death and judgment that comes with Jesus' return as the judging Son of Man (17:37)."399
The general teaching of the parable is that Jesus' appearing and the beginning of the kingdom will be sudden and unexpected by most people who are alive then. It will be an unmistakable event in history and will involve physical danger for earth-dwellers because divine judgment will follow immediately. No one will be able to miss it when it occurs. Jesus did not say exactly when it would occur, but clearly it would not happen immediately. An interval of time would have to elapse.