The 2 options are to allow everyone involved on the project communicate with the client, or to restrict access so that only the project manager (and selected team members) can communicate with them.

In the case of allowing everyone access, it means that communicate is more open and encouraged, but is there need for the customer to interact directly with all the members of the team? The general response from people is no, and David made another great response in part of a comment, which is shown below

Tickets:
Good idea but obviously should not be visible to the other users, only the PM. The customer shouldn’t be able to just throw something new in. It should be communicated to the PM and then pending the PM’s approval, the PM can add the needed tasks. The customer throwing a new requirement in can create a new for new resources, require additional funding, adjust the schedule, or adjust the scope of the overall project.

Basically, if a client can communicate directly with the team, they may try to get changes into a project which need to be reviewed by the project manager. This can happen in both tickets and tasks. As a result, it is best to initially restrict access to everyone but the PM and allow them to choose to allow certain users access or to share certain messages.

This adds another layer of complexity as before showing any message, it needs to be cross referenced with a list of users that can see that message. Although this is not much of a cost in terms of implementation, it may have a negative impact on performance.