Depending on the process you live in your team it maybe required to allow users to reply on tickets, even if they are not having the lock or not being the owner of the ticket.
Be careful on this setting!
Since the ticket system is ensuring, that no concurrent changes are done without having the requirement to have the lock on the task. E.g. assume a client and a client colleague call your team and two persons are now working in parallel on the same ticket. With the lock, the agents would identify that someone is already working on it. But without, both agents are now able to work on the same ticket and possibly will create a mess on the client side – and – of course on your side!