What is a reason the number of metrics in the plugin.json file can differ from the number of billed custom metrics?

The reasoning behind the choice that the number of metrics in the plugin.json file can differ from the number of billed custom metrics is that plugins in Dynatrace can generate "splittings" for additional dimensions.

When custom metrics are created using plugins, they often include a base metric that could be segmented or split into multiple dimensions based on various parameters such as tags or attributes. Each of these splits counts as a separate custom metric for billing purposes. For instance, if a plugin defines a single metric and that metric can be split by host, environment, or other dimensions, each unique combination created through these splits will result in additional billed custom metrics, hence leading to a discrepancy between what is defined in the plugin.json file and what is actually billed.

This ability to create additional dimensions through splitting allows for more detailed analysis and reporting. However, it can also result in a higher billing count for custom metrics, emphasizing the importance of understanding how plugins are configured and the implications for billing in Dynatrace.