Yes. Activating view all user's clients / reports for a Writer user will allow them to:

• View and edit the existing clients and reports of all users within their account; as well as
• Create new clients; and write new reports for all users with their account.  

It is possible to restrict which clients / reports certain users within your account can view and edit using Workgroups. Workgroups are particularly useful if you have different offices or departments within your company, and you only want users to be able to share their clients / reports with other users within their particular office or department.