stable-rc optimizations, less often builds or build on trigger?

[nuclearcat]

It seems our trigger are being often caught up in the middle of stable-rc updates, they might update tree during more than 1 hour, and we often unnecessarily retrigger the build. As i remember, there was discussion that it is not necessary to test tree on every change, but only on some email (?). This will help to reduce load on build cluster: