Besides preventing you from being able to reach Esthar, it's role in the story was the site where Lunatic Pandora was excavated.
That's the second time you've said that in this thread, and it doesn't make it any more true than it was the first time.
The save menu location bar quite clearly marks the area as *Centra* - Excavation Site. Furthermore, Laguna talks about his "grand escape from Centra" when we next see him in Winhill. The Excavation Site was in Centra, not Trabia.
In addition, Lunatic Pandora was never excavated. It is the Crystal Pillar that was excavated and the Lunatic Pandora immediately built around it (in order to seal and control its abilities). The Crystal Pillar is solely responsible for the calling down of a Lunar Cry, and it caused the Lunar Cry 80 years before the start of the game.
However, it has been stated that several Lunar Cries have also occurred in the past. In the absence of any alternative explanation, it's not a huge reach to say that the Trabia Crater, plotwise, was caused by a past Lunar Cry. Of course, how all this and Tears' Point comes together is something that we'll likely never know.
But yes, the crater's main purpose is to prevent early entrance into Esthar's territory.