Oneagent provides visibility into much more than just the Application processes. It also provides infrastructure and OS level metrics. For example, CPU load, NEtwork load, disk load, all divided by the consuming process. It also provides visibility into what processes are talking to other processes in your enterprise. So you can easily see all the processses that are connected to your Oracle instance as well as any connections your Oracle instance makes out to other processes.
All this information is fed into DAVIS, our AI engine which provides the ability to determine root cause easily across the enterprise.
As for CONs: Other than a few CPU cycles to run the agent components, I don't see much that fits this category.