I've just paid attention to structure of 3D-model of compression spring generated using DA (Design Accelerator).
Result is the assembly containing subassembly.
Subassembly consequently contained the only part.
...a bit complicated as for me, but...
Using just the part itself makes it impossible to edit later the spring with DA.
Using the subassembly within other assembly - the same - can't be edited with DA.
...just for satisfying curiosity...
What makes Design Assistant "understand" which component can be edited and which can't?