Some people thrive when bugs are assigned to them early, some people thrive when whole new functionalities are assigned to them. Usually intersection of sets of these two kinds of people is close to empty and the worst mistake is to assume bugs first are good or new stuff first is good automatically.
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.
Our team always assigns a few cosmetic bugs to new developers during their first week - only because it helps them learn their way around our codebase.
Where they proceed from there depends on their strengths and interests.
I like both as long as they as smaller items. Bugs will help you to understand what is there and new functionality can be a good bridge where a new person can leverage existing experience.
