The rarely used and often misunderstood CAD client finally made it onto the ESRI deprecation list. The CAD client allowed a way for AutoCAD users to connect directly to ArcSDE and both view and edit CAD data could be loaded directly into ArcSDE as a layer using the command line loader. Several years ago I loaded an entire cities worth of utility data into SDE. I could use an ArcIMS ArcMap Image Service to create a simple web site. What was so great about the solution is that the surveyors could edit their SDE data from AutoCAD and those changes we're reflected in the ArcIMS site. There was no ETL. There was no custom programming. There was no data conversion. Companies frequently try to achieve that level of integration and automation with far more expensive and complex solutions.
For the last several years the fate of the CAD client had been in question which made it something to avoid. We've known that this day would come, but I'm sorry to see it finally go.