Your question is Scaling Horizontal vs Vertical. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Describe the difference between horizontal and vertical scaling in a distributed database environment, and when you would choose each for MongoDB workloads.
Compare the operational, performance, availability, and cost trade-offs of each approach. Explain how MongoDB replica sets and sharded clusters affect the decision, and identify workload characteristics that would influence your recommendation.