[maccard]

> The drawback is that sources from the jumbo can not be compiled in parallel. So if one has access to extremely parallel compilation farm, like developers at Google, it will slow down things.

Generally the way this works is rather than compiling into one jumbo file, you combine into multiple files, and you can then compile them in parallel. UE4 supports it (disclosure, I work for them). and it works by including 20 files at a time, and compiling the larger files normally.

There is also a productivity slow down where a change to any of those files causes the all the other files to be recompiled, so you can remove those files from the individual file.

> The compilation time saving can be up to factor of 2 or more on a laptop.

The compilation time savings are orders of magnitude in my experience, even on a high end desktop. That's for a full build. For an incremental, there is a penalty (see above for workarounds)