One school of though: distributing built files is a waste of time, since the means exist to generate them on the target machine.
The other side of the coin: All the arguments on the previous slide about being nice to the package builders.
Common result: both source and built files are distributed. Users can then regenerate things from source, but this is not required.
Note that this last point is not universally true. Some package maintainers will only distribute the built files and not their sources. In practice, this is probably the worst case, although it does make the distributed tarball slightly smaller.