I cannot speak to the merits of Datadog as I looked at it a long time ago. New Relic's strength is that it will help you collect the performance of code and provide strong analytical capabilities. If you know the code base you can instrument the code and get monitoring data…
I believe the other responses capture the use cases sufficiently. APM tools allow you to measure the performance of your code as well as capture exceptional information about the errors etc
To address the who part of your question: people in these roles could benefit from…