I thnk we're all talking past each other. There are
three things at play here - a fully constrained sketch,
strong dims and locked dims.
Fully constrained simply means that every sketch entity
is positioned to existing geometry or datums. You cannot
create a sketch in Pro/E that is not fully constrained
because Pro/E will add dims to constrain the sketch.
Those dims will be weak, but they still constrain the
sketch and define how it will behave when the underlying
geometry changes.
Weak dims then are simply the dims that Pro/E adds to
constrain the sketch. There is no difference between weak
and strong except that Pro/E will remove weak dims
without warning if a sketch is over constrained. Strong
dims require user acceptance for Pro/E to remove them.
Locked dims behave similarly to strong dims in that you
have to accept their removal if the sketch becomes over
constrained, but additionally will not allow the
dimension value to change by dragging the sketch. Strong
and weak dims will.
Personally, I want all dims either strong or locked as
this tells the user that the sketch is as I want it, not
as Pro/E made it.