One also has to give consideration to when it is OK and not OK to be dodgey.
The established rules for things like DMX allow a system to be built and maintained by different people over time. They don't need to be aware of previous anomalies and system-specific constraints.
Any sort of permanent installation should play by the rules. The next person along shouldn't have to "discover" the Improvised Electronic Devices (IEDs) you have left behind.
If you are throwing something together for an evening and through poor planning (or a lost box of equipment) a y-split or two will save the show, go for it. You know what you have done, you will troubleshoot it and get it working, nobody else needs to get their head around it, and in six hours it'll all be torn down and packed up never to be spoken of again. :-)