Are you sure? I have never interpreted it this way and it is the first way I hear this interpretation.

My understanding: To use something "for real" on an actual project, not just toy around with it. (What you use can be good or bad, expression doesn't say)

My interpretation has always been the same as mceachen's, but other comments in this sub-thread have thought me I am wrong and your understanding is correct. Today I learned.

For what it's worth[0]:

> If you do something in anger, you do it in a real or important situation as it is intended to be done, rather than just learning or hearing about it

[0] https://dictionary.cambridge.org/dictionary/english/in-anger

No, it's a military term. Firing a cannon in anger for instance means firing at the enemy, rather than in training.