It is not quite clear what you want to achieve or avoid. Do you want to make sure that the same account can not log in to several machines, or are you worried about files being modified on several nodes?
If the user has its homedir centrally in SMB, a login to a second node while he already is logged in with the same account elsewhere will give rise to problems since Apple does not use file locking in a systematic manner and the Macs will happily try to modify plenty of files (caches, preferences,...) that are already open by another Mac. Some apps appear to use file locking, and that will make the login of the second session very slow. The state of the files touched by apps that don't use file locking is undefined. Another potential issue is ~/Library living on SMB and logging in from Macs with different OS versions. No need to be logged in to several nodes at the same time to have problems with incompatible versions of files and databases in ~/Library. Been there, tried that. Gave up on using SMB home dirs.
Portable home dirs are not supported any more, so no need to discuss that scenario.
For local home dirs it doesn't really matter on how many Macs a user logs in as all files are local - except if you have invented some way to sync back changes to a central place. I am not aware of any way to prevent logging in to several nodes at the same time.
Hope this helps.
