I have ran a simulation of a protein structure using Gromos force field and obtained the radius of gyration. Is it mandatory to get a linear plot? How does high or low RoG matters? What it implies if RoG changes during simulation?
"How does high or low RoG matters?" - RoG gives you a limited information (limited because it's just one number) about the shape/size of your system.
"What it implies if RoG changes during simulation?" - small RoG changes imply that the system is stable in the sense of not changing its shape/size too much; large RoG changes imply that the system changes it's shape/size (likely conformation) during simulation.