This picture shows the difference between a two person team and a one person team regarding the ownership of schedule, cost, and quality.

1. Quality
Schedule Cost
Complicated non-linear relationship. These 3 critical
project variables are inseparable
Schedule Cost Quality
Is Responsible For
Is Responsible For
UNNECESSARY
FRICTION ?
Project Manager Project Engineer
(Project Plan) (Technical Plan)
Quality
Schedule Cost
Responsible For
Much better chance of
achieving a balance
between all three critical
factors when one person is
Project Manager
holisticly responsible for
(Project Plan)
all 3.
Project Engineer
(Project + Technical Plan)