[otrs] Old accounts - customer users and users

I understand that you can invalidate old accounts as deleting them creates a number of issues. However as the number grows there become a practical limit to having a gross of invalid accounts (Doesn't it?) What problems could be expected should I edit and existing account for a new user? As I understand the design the existing account details will remain as the account details are stored in the article/job/ticket tables? Will this allow the new user to "see" old unassociated tickets? Appreciate your thoughts and comments. L.Q. Marshall