Even after we have created our SOLIDWORKS assembly, we can convert parts and subassemblies into a new subassembly. This is particularly useful when we design our model from a Top-down assembly method.
We can simply select the components that we want to be combined into a new subassembly and select Form New Subassembly. SOLIDWORKS will even maintain the mates that have been applied.
However, we have to be careful with any existing references to the parts that have been converted to a new subassembly. As the new subassembly will have a new name, the reference might be lost.
The new subassembly is also stored as a virtual part, simply select Save as External File when needed.
This allows us to design using a Top-down method and gives us the flexibility to form new Subassembly for drawing purposes.
We can also dissolve our subassembly in the same manner.