The term "Final" in signifies that this was the last, most stable build of the Lightroom 4 lifecycle. Before Adobe moved entirely to Lightroom 5, this version was the culmination of every bug report and feature request from the previous 4.0, 4.1, and 4.2 releases. It was the version photographers installed and forgot about—because it simply worked.
Furthermore, the lens profile database saw massive expansion. Lens corrections are vital for fixing geometric distortion (barrel distortion) and chromatic aberration. Version 4.3 introduced profiles for popular lenses such as the Canon EF 24-70mm f/2.8L II USM and various Nikon AF-S lenses, ensuring that raw files were automatically corrected upon import. Adobe Photoshop Lightroom 4.3 Final