When account A has logged into computer A, and then account A starts to log in to computer B, account A in computer A will automatically be logged out. May I know what are the possible reasons in why this feature should be implemented? How does it make it more secure?
From the perspective of a developer who recently has to implement such a feature, another possibility is to prevent the users shooting themselves in the feet.
Many custom/internal applications have very specific workflows and store a lot of state in the session. If the user abandoned some work halfway on one computer, finishes it somewhere else and return to the original computer, he/she may get confused about the unifinished work. If the user incorrectly chose to continue, then the original results may be overwritten / duplicated.
It is of course possible to improve the code to make this less likely, but for an internal app, the most cost effective way is to prevent concurrent logins.