When should you branch?

Question

When working with a SCM system, when should you branch?

Answer 1

I find the advice from Laura Wingerd & Christopher Seiwald at Perforce is really concise and useful:

* Branch only when necessary.
* Don't copy when you mean to branch.
* Branch on incompatible policy.
* Branch late.
* Branch, instead of freeze.

See http://www.perforce.com/sites/default/files/pdf/perforce-best-practices.pdf for a detailed explanation of each of them and other best practice.