Pls explain IFM(In-Flight Modification with simple example. when will use IFM

IMF refers to the concept of updating active instance in-flight meaning when the process instance is still in active status, typically we do this for dev work to avoid multiple saves of the model or in higher environments for having a temporary workaround fix for that instance flow. Manually this can be done via edit process view for an instance where we can modify flow and variables for that particular instance, where we can have full features for editing. If we want to do this in bulk and for minor changes, we can use IFM Manager plug-in, you can find the documentation for that here - IFM Manager