Every container you run in Kubernetes is going to be generating log data. No one has time to go through and regularly check individual container logs for issues, and so in production environments, it is often required to export these logs to an aggregator for automated analysis.
If you're using Azure, then Log Analytics may be your log aggregator of choice, and so you need a way to export your container logs into Log Analytics. If you are using AKS, you can deploy the Azure Monitor solution which does this for you, however, if you are running your own cluster, or even using another cloud provider and still want to use Log Analytics, then that it's not quite so simple. This is where Fluent Bit can help.