Consider using shared SSTATE, it saves you from all the rebuilds,
while keeping Yocto internals intact and sane.

We are using sstate cache, but if I am not mistaken it can happen that even though a package is in the sstate cache, there's a cache miss and the package gets rebuilt - and this is exactly what some coworkers would like to avoid, cause it means a different binary is on the target than the one previously built and tested. That's why I posted another question here (maybe 2 weeks ago) if there's a way to force Yocto to only use sstate-cache and fail if a package needs to be rebuilt or to print a list of packages which were built from source. But there's no an "easy" way to do it.