We have a sourcesystem table, each source is defined. We needed the ability to enable/disable sources and this accomplishes it, and leaves us a trail in case something strange happens (Super Storm Sandy forced a data center there to close, no problem, I disabled the source to prevent pkgs from looking for it).
Further, all the auditing carries this sourcesystemkey. We host, so it is critical that I be able to determine very quickly where a problem is coming from.
Strongly agree on the auditing, also. It has saved my butt many times. Every table has an audit key from which I can determine when it ran, what sources it hit, how many records returned from each, dimensions referenced with hits,misses, unknowns, etc etc.
Lastly, Event Handlers. While easier than expected to implement, this also has saved my butt many times. When there is a problem and we need to consider killing pkgs, I can consult my logger to see what step every executing pkg is in. We had some delete before insert pkgs so would not want to kill past delete before insert but never knew quite where the pkg was. Now we know.
Build this stuff out sooner rather than later.