I have found this useful on several occasions when I have wanted to make the file size of a SOLIDWORKS part smaller - especially if I want to email it and I am tight to a limit.
The method is dead simple - simply create a feature that encloses all other features. I usually use an extruded rectangle and extrude 'Through All' in both directions. Then save it and check the file size. The size will reduce a little for simple parts but by a lot for complex parts like mouldings or parts with lots of patterned features. The reason for this is that the file will include the definitions of all the visible faces, edges etc along with the features that were used to build them. If the part is one monolithic block then the number of visible faces is significantly reduced and the file size is smaller.
To rerverse the process, you just need to inform the receiver of the part that he/she must either suppress or delete the last feature in the tree - don't forget to tell them or they will get very confused!
Here is an example. The plastic drill was 2.38MB before the addition of the block and 1.56 MB after - reducing the file size by 35% compared to the original size. Here are 'before' and 'after' images.