It can be useful to be able to stop transactions being posted before a certain date. For example, to prevent colleagues from posting into a previous month or year that you've finalised, or simply to avoid the common mistake of entering the previous year during January.
In Sage 50 Accounts you can set a lock date so a warning appears if anyone tries to post with an earlier date. For each user you can choose to block postings altogether, or simply show a warning that can be overridden.