Why must there be a NEED? Why did we ever send ships across the ocean to explore? Where was the need? People like doing science, and so we're doing science.
That was (for the western hemisphere) mostly to steal gold and silver from other civilizations. Oh, and to grow addictive drugs for export, like in Virginia. It was never done for other than banal reasons, although I'm sure pious rationalizations were offered to make people feel better about the ongoing genocides.
Wasn't it to discover alternative trade routes and also to show physically that the world is round? I think they didn't know that there were usable land to grow tobacco when they started.
The first of those is banal, and the second is wrong -- they already knew the world was round, and had a more accurate estimate of the diameter than Columbus was claiming.