One reason for using Conversion Optimizer is to:
• Avoid unprofitable clicks.
• Generate more clicks than manual bidding would generate
• Dynamically manage ad position
• Maximize ad exposure

Correct Answer is:

• Avoid unprofitable clicks.

Explanation: Conversion Optimizer works best for advertisers whose goals are mostly conversion and direct-response oriented.

You can read more here:

https://support.google.com/partners/answer/2769753?hl=en