Freezing the User Record:
                Freezing the user record means to temporary not allow the user to access the company’s confidential information. So it is basically temporary suspending the user so that as an Administrator you can do more work before deactivating the user. It will not make the user licenses available for use inside the organization. Freezed users can be unfreezed also.
Deactivating a User:
                Deactivating a particular user record means that user will no longer be able to access company’s confidential information. When a user is deactivated, their user licenses become available. Inactive users can still own all their data. As an administrator, you can transfer the ownership of the data. Typically, ownership of inactive users kept as it is to track the history later. Deactivating a user will remove the user from all delegated groups and sharing privileges. During deactivation process, you will have the option to keep/remove the deactivated user from the team.
Deactivating a user may fail due to below reasons-
·         If the user is an assigned leads or cases as part of Assignment rule.
·         Sole recipient of a workflow email alert.
·         Default workflow user.
·         Default lead owner.
·         Default case owner.