Feature flags are a good example. One developer A enable a feature and deploy its version on integation.

Two days after, developer B deploys its version, but isn't aware that A deployed with the new feature enabled, so the feature is disabled with its deployment on integration.

Ideally, developers should use a centralized configuration management to no suppress each other configs. That's why we use Jenkins or the Atlassian suite for example. But it's heavy to install and maintain sometimes.