If you change the value of a dimension, the size and shape of the 3D model change and the 2D drafting views update accordingly. You can also create assemblies from these parts. If a part changes, the assembly updates. These programs are aimed primarily at mechanical designers. Probably the most significant difference between Inventor and the other products is not apparent to most users.
Inventor takes a completely different approach to managing data.
Theoretically, nothing limits the number of parts that you can include in an assembly, but other modelers generally bog down and become very slow when an assembly contains a few hundred parts. Inventor, however, easily handles assemblies with several thousand parts. Release 4 enhances this capability even more by letting you partially load an assembly. Another unique feature of Inventor is its adaptive assemblies. Parametric modelers update an assembly if a part changes.