It's a project that started in the late 80's to resolve some rendering conflicts in low resolution printers – which, despite the passage of time, is still as relevant today, just moving the concept from printers to the screen.
The real problem here is that the majority of modern fonts are not designed to behave at the modern screen resolution which is limited in DPI depth – and while more true for the first screens with 72, 96 dpi – it's still true for the 400, and upward, dpi. They were designed to use more than 1500 dpi in the print world.
It's the old Raster versus Vector: Dawn of Rendering battle – where fonts are described as vector-perfect lines and curves – which are then converted to raster pixels on the screen.
Basically every letter gets drawn again at each point...