Statistics Collection Recommendations – Teradata Database 14.10 - comment by carrie

Armin,
If you haven't seen it, take a look at my blog posting Statistics Threshold Functionality 101.  That may provide a little more understanding about how to use threshold.
In general, the recommendations are to rely primarily on the system threshold option, SysChangeThresholdOption.  You don't have to set that, but it does require that UseCount logging be on for the database.

1. Turn on USECOUNT logging in DBQL for all databases for which statistics are being collected and where you are relying on system threshold, otherwise it will not do anything.
2. Use the statement-level threshold only for special statistics that need to be handled differently from the system default or the DBA-defined global defaults.  Favor percent of change over number of days as your first choice for the type of threshold to use. 
3. But if USECOUNT is not being logged, then rely on time-based thresholds and set DefaultTimeThreshold at your preferred number of days. 

Thanks, -Carrie