I used neither for the most part. I designed almost everything in place. Before starting on this project I spent quite some time analysing various imagery for the Hatchetman mech, and figuring out the scaling, spacing, and over all volumetric needs of the various aspects of the mech (ie arms, legs, chest, etc). I have several pages in my sketchbook devoted to understanding the proportions and alignment of parts, both in detail and in the abstract. From there I was able to block out the general shapes as individual groups, which I could then go into individually and modify. In sketchup there is an option to change weather or not an item outside of a group is visible while working in a group. I routinely work with the option to turn all objects outside of the group invisible. This keeps other items from obstructing my view and reduces the need to move parts out of place to work them.
There were times when I needed to pull copies out of place when I was not happy with the particular geometry of a part so I could work on it next to the original, or even a third or fourth copy where I worked out various ideas. In those times I would space things out a certain amount along a specific axis so I could easily move the part back into the original work.
