Waterfall Model is a flow based model, in which we pass every phase once and cannot go back to that phase again. Its most eminent drawback is that if there is any change is requirements, we cannot make any changes to the requirement section. 

 
Advantages of Classical Waterfall model:-

1.Easy to understand.

2.Useful and known.

3.Define before design,design before code.

4.Works well.

Disadvantages of classical Waterfall model:-

1.Dose not match with reality.

2.Expensive to change documents.

3.Software development delivered late.

4.Difficult to manage.


In case of Iterative Waterfall model we can always come back to previous phases,and make the changes accordingly.

Advantages of  Iterative Waterfall model :-

1.It has feedback path from one phase to its previous phase. So easily it correct its error and change the document.

2.It is very simple to understand and use.

Disadvantages of Iterative Waterfall model:-

1.Incremental delivery not supported here.

2.Overlapping of phase not supported.

3.Risk handling not supported.

4.Limited customer interactions.