When you give someone new functionality to implement and they don’t have experience fixing defects, they’ll likely add more defects along with the new functionality.
I am in the group that prefers new functionality; I can build state-of-art $10M business from the scratch in 3 months but if you ask me to debug old stuff for longer periods of time, I'll most likely leave or underperform. It's good to know what people you have on your team instead of assuming certain traits.