What would you set up to collect how many comments users posted to a webpage on your site?
Custom Channel Groupings
custom metrics can produce more flexible and more readable custom reports and as such are a convenient way to track your most important metrics.
Read more here: https://support.google.com/analytics/answer/2709828?hl=en#example-metrics
Similar to custom dimensions, custom metrics can have different scopes. Hit-level custom metrics get associated with all the hit level dimensions with which it was sent. Similarly, product-level custom metrics are associated only with the product with which it was sent. The following examples illustrate these two types of custom metrics.
Hit-Scoped Custom Metric Example
In the examples above, the game developer has been tracking each play of a level as a screen view. In each of the reports generated, the screen view metric is used to represent a player’s attempt to complete a level.
However, the developer also wants to know the completion rate of each level.
To determine the rate of completion, the developer will use a new custom metric called Level Completions and compare it to screen views for each level.