Difference between ant all and ant clean all in hybris - Hybris Interview question

ant clean all	ant all
Delete all model classes create again.	Does not delete model classes but create new ones if required.
It checks whether config,log,data,temp etc folders are available inside hybris folder. If this folder structure is not available then it creates the folder structure	It assumes folder structure is already exist
If there is no build, It will create a build from scratch, if there is any build exist, It will delete and recreate it	If there is no build, it will create a build from scratch, if there is any build exist, it will modify it rather than recreating it.
Slower than ant all as it delete classes and folders and regenerate them.	Faster than ant clean all
Is advised to use only when there are changes in items.xml file	Is advised to use for every build.