Ollie wrote:

The question was, when to use the shaping cutters and when to
use the routing bits in the same machine.

snip

In some cases, the shaper table size is not large enough and
you have to use the dado blade in a table saw. The essence of
the question is for those cases, where you could do the same
cut either by shaping or routing. For example, there could be
some reasons to use a cutter head for shallow dados and a
routing bit for deep dados. What are the resons for dado
cuts? What are the resons for other cuts?

A simplistic response: For those cuts you'd make at or slower
than 10,000 RPM with a router, use the less expensive bit. If
10,000 RPM is too slow for a router cut, use the (generally
larger diameter) shaper cutter.

You might find it helpful to DAGS on 'router chip load' - which
is one of the relevant tool factors (others are feed rate,
spindle speed, and cutter geometry) - and, of course, the
material being cut has considerations of its own.

These days my shaper sits idle and a 5HP router does the work.
For most of the work I do, I run the spindle at 18,000 RPM and
feed somewhere between 1-1/4" and 1-1/2"/second for burn-free
cuts with a minimum of dust. I generally consider that I have
things fairly well balanced when the routing operation produces
chips (with a length equal to the depth of cut) rather than dust,
and a nice clean edge with no burning.

Not sure I understand your last two questions - Cut a dado when
your design calls for a dado. Cut something else (or not at all)
when a dado isn't called for.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/solar.html