Log retention
A new Log retention setting has been added to Log settings:

Using this slider you can configure how many days you want to keep messages in a specific log. Each subscription plan comes with overall retention, but in scenarios where you want to lower this for one or more logs, you can use this feature. Examples could be a development log where you only want to keep messages for a few days or in regards to logs containing personally identifiable information that you are only allowed to keep for x days.
Lowering the log retention will not help in regards to keeping beneath your monthly message quota, since that is calculated from how many log messages get received and stored and not when they are cleaned up.