Question

I have read much information about agile and waterfall and I just cannot think of any reason why someone today should do the waterfall. I am concerned especially about testing process.
Do I miss something, is there some clear advantage that I have overlooked?

Answer 1

There are still cases where waterfall is appropriate. Canonical examples include military, space, medical and safety-critical systems such as flight control software where you absolutely need to determine the spec first in exact detail, develop it, then thoroughly test the complete product.

Agile works for most business and product software (i.e. the majority of software built) because it allows users to start with a rough idea and refine it as they go along. If their website or internal line-of-business application isn’t quite right (or has bugs) for a few iterations then it is generally outweighted by the business value that’s delivered quickly from the bits that do work. You wouldn’t want to start with a rough idea for a nuclear power plant controller system and refine it as you go along.

The trade-off of using pure waterfall is that it is orders of magnitude more expensive to develop software in these scenarios. However, the cost-benefit is still favourable since you cannot afford for (say) your spacecraft to hit a null pointer exception halfway into orbit.

There are of course shades of grey in between. It is possible to use Agile techniques within a waterfall framework (see RUP) and the balance can be scaled up and down between pure waterfall and pure agile.