Uses
Typically RMSD is used to make a quantitative comparison between the structure of a partially folded protein and the structure of the native state. For example, the CASP protein structure prediction competition uses RMSD as one of its assessments of how well a submitted structure matches the native state.
Also some scientists who study protein folding simulations use RMSD as a reaction coordinate to quantify where the protein is between the folded state and the unfolded state.
Read more about this topic: Root-mean-square Deviation (bioinformatics)