For the most part I tend to use a variety of different techniques.
I generally have some sort of layout sketch, such as a general plant
arrangement layout, a conveyor layout, etc. I will put this into a part
file so I have more leeway as to hiding, suppressing, moving, etc in the
assy, and mate it into the assy with something major at the origin.
Depending on what the job is, this may be a column line, or it could be the
center of a transfer - a work point - just depends. I may have a car body
outline part that has three sketches in it - front, side, top, again mated
in whatever fashion is appropriate. Then I usually find that as my design
progresses, I may add some sketches in the assy to help define the location
of something, or give me some ref dims to watch as I work around something
else. These are all the basis of whatever I am designing.
Then I start with something like the carrier that will handle the body.
This will go into the assy in such a way as fits the scope of the job.
Maybe I want to be able to move it along a path and see how it chords around
the curves. I may have a fork transfer that moves the car from an inverted
carrier to an overhead carrier, and that transfer is mated with its system
planes to the assy, usually to part of the layout sketch. I might have some
tooling that travels with the carrier, so it gets mated to the carrier in
So, as you probably already know, there isn't one right answer, and probably
not always even just one that fits the job. Having many tools in the box,
and enough experience to know how and when to use each one, generally leads
to a better SW experience.