How do you eat an elephant? One bite at a time!
Likewise, agile development projects are delivered in small bite-sized pieces, delivering small, incremental *releases* and iterating.
In more traditional software development projects, the (simplified) lifecycle is Analyse, Develop, Test – first gathering all known requirements for the whole product, then developing all elements of the software, then testing that the entire product is fit for release.
In agile software development, the cycle is Analyse, Develop, Test; Analyse, Develop, Test; and so on… doing each step for each feature, one feature at a time.
Advantages of this iterative approach to software development include:
For this approach to be practical, each feature must be fully developed, to the extent that it’s ready to be shipped, before moving on.
Another practicality is to make sure features are developed in *priority* order, not necessarily in a logical order by function. Otherwise you could run out of time, having built some of the less important features – as in agile software development, the timescales are fixed.
Building the features of the software ”broad but shallow” is also advisable for the same reason. Only when you’ve completed all your must-have features, move on to the should-haves, and only then move on to the could-haves. Otherwise you can get into a situation where your earlier features are functionally rich, whereas later features of the software are increasingly less sophisticated as time runs out.
These are important characteristics of iterative, feature-driven development – and they’re essential if you plan to deliver in fixed timescales – one of the 10 key principles of agile software development.