I would like a case for Waterfall and other SDLC models , and see whether the Agile Process actually can be fit in somewhere or all practices under agile must go together. For instance till design we iterate with Agile and then do waterfall to deliver.
If you're trapped in an unhealthy waterfall schedule, say with 8 months of coding and 12 weeks of QA (from experience), you can sneak some agile ideas in and make life better. Break a handful of giant use cases into dozens of small features visible to the user. Break 8 months of coding into 17 iterations with full build, integration and internal release. If you have a couple customers or QA folks who are mature enough to look at unfinished systems they can help validate the internal releases.
I would definitely not recommend anybody set out to design such a process on purpose. It isn't "genuine agile" and it isn't ideal, but it might be a first step out of the primordial ooze.
A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi