For runtime patching: I needed that twice: First there was a bug in the stdlib event log logging for windows which crashed when the user was not an admin (2.7 days). We could monkey patch that problem on the fly which was much better than any alternative.

Second I needed to redirect scikitlearn logging to a file. Which did not work because scikit does not use logging but something homegrown. We just overwrite the internal log function and all was good.

Yes it's seldom needed and it's a very sharp sword but it's much better that it's there when you need it. I encountered bugs in .net stdlib which where there was no alternative than to wait for the next release. Very ugly when you need to ship.