What happens when we remove SID history?
Domain Migration Administrator 7.x
After removing SID history, target users no longer have access to files on a file server where security has not been translated.
Domain Migration Administrator actually clears the SID history attribute that corresponds to the source account from the user and group account objects in the target domain. Subsequently, the user will lose access to any resources in the source domain for which security has not yet been translated. Therefore, we always recommend that you translate security (for example, using 'Translate Security Settings' wizard) before removing SID history, as noted in Chapter 7 of the User Guide.
You can use the Remove SID History wizard at the global level in Domain Migration Administrator (DMA), or within a DMA project. Since SidHistory is an attribute of the target account, you should be logged in with an account that is an administrator in the target Active Directory.
Please note that this information can also be obtained from Chapter 2 of the DMA and SC User Guide.