Easy to understand and easy to use.
Provides a reference to inexperienced staff.
Milestones are well-understood by the team.
Provides requirements stability.
Facilitates strong management control(i.e plan,staff,track).
Works well when quality is more important than cost or schedule.
WEAKNESSES:
All requirements are to be known upfront.
Deliverables are created for each phase,and considered to be frozen – inhibits flexibility.
Can give a false impression of progress.
Integration is one big-bang at the end.
Little opportunity for customer to preview the system.