Sometimes though you just want to make the diagram as complicated and ugly looking as possible to get a point across or make a sale. You can't make it look like it's just a bad diagram - you have to give the impression that the author has really tried to make it comprehensible it's just that the underlying idea is bad.
The classic use of this is the IT department trying to get money to do a systems consolidation or re-engineering. The architecture team will dutifully come up with the ugliest diagram of spaghetti known to man, that will get presented as proof of how bad things really are.
Turns out politicians know this trick too; as shown below:
This diagram published by the Republicans on the Joint economic Committee “explaining” Obamacare is a classic of the genre. Undoubtedly high-price (and worth it) consultants have been consulted to make this look so complicated.
High res version here
It has all the classic tools to over complicate something:
Note: For the purposes of this article I don't particularly care about whether Obamacare is overly complicated or not, a good thing or not, it's just an interesting look at how the diagram designed can push messages.