As your company probably does, employers want to see constant growth and progression in one's career. So, staying in ANY job more than 3-4 years is going to start to look like a problem when you are job seeking. Moving up to a new category can change that perception, from Research Scientist to Senior Scientist, or from Senior Scientist to Principal Scientist, etc. But, sometimes people do well to have a variety of experiences, and so moving from R&D to the production facility, moving from lab-scale bioreactors to the large scale production of therapeutics would be one way . . . or, from science to business development, etc.
“Humility is not my forte, and whenever I dwell for any length of time on my shortcomings, they gradually begin to seem mild, harmless, rather engaging little things; not at all like the glaring defects in other people’s characters.” - Margaret Halsey