"Breakout By", tells the alert system at what level of granularity the data should be counted. You can use “Breakout By” to apply the alert rules to every crash message, log type, domain, etc. to avoid creating multiple alerts.
Let's use the Alert Type Crash Count, broken out by Message as an example. If the app has 10 different crash messages and any one of those crash messages exceeds the set threshold, the alert will be triggered.