Don't get me wrong. I'm a big fan of agile software development. If you're a regular reader of my blog, you'll know that :-)

But I'm not so pro-agile that I've lost all sense of balance. An agile approach to development is good for so many reasons. But agile development does require certain things that can also be a disadvantage.

If you're thinking of adopting agile principles, it's important that you know what you're in for. You need to be sure that you, your project team and the management supporting your project all understand these trade-offs, and are happy to accept and support them in preference to a more traditional approach.

Here's my list of potential disadvantages with agile:

• Active user involvement and close collaboration are required throughout the development cycle. This is very engaging, rewarding and ensures delivery of the right product. It's the fundamental principle in agile that ensures expectations are well managed. And since the definition of failure is not meeting expectations, these are critical success factors for any project. However these principles are very demanding on the user representative's time and require a big commitment for the duration of the project.
  
  
• Requirements emerge and evolve throughout the development. This creates the very meaning of agile - flexibility. Flexibility to change course as needed and to ensure delivery of the right product. There are two big flip sides to this principle though. One is the potential for scope creep, which we all know can create the risk of ever-lasting projects. The other is that there is much less predictability, at the start of the project and during, about what the project is actually going to deliver. This can make it harder to define a business case for the project, and harder to negotiate fixed price projects. Without the maturity of a strong and clear vision, and the discipline of fixing timescales and trading scope, this is potentially very dangerous.
  
• 
  
• Agile requirements are barely sufficient. This eliminates wasted effort on deliverables that don't last (i.e. aren't part of the finished product), which saves time and therefore money. Requirements are clarified just in time for development and can be documented in much less detail due to the timeliness of conversations. However this can mean less information available to new starters in the team about features and how they should work. It can also create potential misunderstandings if the teamwork and communication aren't at their best, and difficulties for team members (especially testers) that are used to everything being defined up front. The belief in agile is that it's quicker to refactor the product along the way than to try to define everything completely up front, which arguably is impossible. And this risk is managed closely through the incremental approach to development and frequent delivery of product.
  
• 
  
• Testing is integrated throughout the lifecycle. This helps to ensure quality throughout the project without the need for a lengthy and unpredictable test phase at the end of the project. However it does imply that testers are needed throughout the project and this effectively increases the cost of resources on the project. This does have the effect of reducing some very significant risks, that have proven through research to cause many projects to fail. The cost of a long and unnpredictable test phase can, in my experience of waterfall, cause huge unexpected costs when a project over-runs. However there is an additional cost to the project to adopt continuous testing throughout.
  
  
• Frequent delivery of product and the need to sign off each feature as done before moving on to the next makes UAT (user acceptance testing) continuous and therefore potentially quite onerous. The users or product owner needs to be ready and available for prompt testing of the features as they are delivered and throughout the entire duration of the project. This can be quite time-consuming but helps drastically to ensure a quality product that meets user expectations.
  
  
• Finally, common feedback is that agile development is rather intense for developers. The need to really complete each feature 100% within each iteration, and the relentlessness of iterations, can be mentally quite tiring so it's important to find a sustainable pace for the team.

I believe these trade-offs are well worthwhile. Software is complex. People are complex. And the only thing that's certain in projects is change. This lethal combination of unpredictability is more often than not helped by agile principles. So, in my view, for many project situations, the advantages of agile development far outweigh the disadvantages.

See also:
Is agile development right for your project?
Why most IT projects fail. And how agile principles help
10 good reasons to do agile
10 Key Principles of agile software development

read more