I am not sure if I should use Sprites for creating things like grass. I noticed a Billboard flag and a Upright mode. I think this means you can not rotate a Sprite yourself? I was trying to rotate it myself but I did not seem to get any result.
I wanted to create grass like in Minecraft where it is set up in a cross like way.
Sprites are considered to be 2D objects lying around on the 3D space , planes are real 3D meshes on the other hand.
In real OpenGL terms, their implementation is exactly the same. Imagine however that if you used only planes and you wanted to be presented as sprites you would have to iterate all of them and apply the matrix transformation (costs CPU time). Sprites do this transformation right from inside the shader and for that saves CPU time.