Sometimes, You Just Need to Slow Down

mitigate this risk. The advantage is a simple, lean codeline structure that reduces the effort spent on the integration of changes. In this model you trade effort spent in integrating changes between codelines (which requires work that adds little direct value) with effort spent writing and executing tests that validate that the codeline still works. These tests may require more effort overall to write, but they provide lasting value to the development stream by allowing for continuous validation that the code works.

Continuing to work on the active development line includes quicker feedback about how well the changes integrate with the active code base, and less overhead to the development team related to merging and propagating changes to the new development stream. Working on one codeline will allow the existing development stream to benefit sooner from the improvements done in service of the task work, and provides more rapid feedback about the reward and risks of the new feature work. This is consistent with the principles of lean branching.

SCM: Change Enabler
An SCM process can use its responsibility for Configuration identification, Configuration control, Configuration status accounting, Configuration authentication as a way to facilitate change or hinder it. By providing the mechanisms for ensuring that the active codeline is evolving in a healthy way, an SCM process can enable a team to deliver more value in a lightweight way.  An SCM Process can facilitate change by:

• Providing for a continuous integration process that validates that each change to the code maintains functionality, and notifying the team when something breaks.

• Generate metrics around failing and passing tests, and use these to guide your process.
• Generate metrics around test coverage and use this to verify that new functionality is covered by automated tests and that changes are related to desired functionality.

Branching has a place in your SCM process, but it's not the only tool you have to provide the change management that SCM is responsible for. It's important to remember that change management and change control are not synonymous. By simplifying your codelines and using tools other than branching to manage change, SCM can help agile teams manage change effectively.

References
[SCMPatterns] Software Configuration Management Patterns: Effective Teamwork, Practical Integration by Steve Berczuk with Brad Appleton
[SIMPLE] Four Rules for Simple Codelines http://bradapp.blogspot.com/2008/06/four-rules-for-simple-codeline.html
[LEANBRANCH] Lean Branching. http://bradapp.blogspot.com/2006/01/lean-principles-for-branching.html and
[ENTROPY] Software Entropy. http://www.pragprog.com/the-pragmatic-programmer/extracts/software-entropy