That's hard to say, and impossible to isolate into a single feature. I like the ability to collaborate either using symbol/layer referencing or Project Sharing. I like the streamlined design workflow. As a set designer, I can 'sketch in Vectorworks, turn the sketches into rendering, finesse the details, improve the renderings and create working drawings for the shops. I like the ability to collaborate, modify the model and have the modifications flow throughout my documentation. I like being able to share the model with the lighting designer (when I'm not also the LD) and the sound designer.
I think it's critical that we all work together to ensure smooth and safe installation.
The addition of Vision and the integration with Lightwright helps all off the design team, and the entire production team, not just the LD.
Vectorworks assigns classes to parts of/types of spotlight lighting devices. I would generally want to assign my own class structure. With objects like doors and windows there are drop downs for class assignment. I would like a choice to assign one class to all (allowing exceptions for glazing), I would like to be able to impose my own classing on object types like renderworks cameras, drawing labels, etc.
Just get it. Vectorworks Designer is a great suite of tools for all kinds of designers.
I think the workflow in one application and the coordination with clients and colleagues is the greatest benefit.