Sometimes it's useful to be able to add notes to a ticket while another user is working on the ticket. e.g. Agent B is assisting Agent A with a ticket and needs to add some information relevant the case to the ticket. Currently this is only possible while if the user that originally locked the ticket unlocks it.
Official response
Lara Proud
You are now able to add Agent Notes to tickets that have been locked by another agent whilst it is still locked, this change was made to enable even smoother collaboration on tickets without the risk of collision.