Why we reuse the same event as much as possible?

Some events capture different versions of a similar action - rowGroupOpened is one such event. However, the reason we don't add separate events is because these functions follow similar logic, and we provide fields in the params object so you can differentiate between results for your custom code in the event. In the case of Master Detail, you can use an if statement to check.

if(params.node.detail) {

// Custom code here

} else {...}