Best practices and my recommendation is that you add your personal email address (that you are not using for a licensed seat) as a collaborator to view plans and test. This way you can actively make changes to the plan as a user, and view the plan as a collaborator side by side so you can see changes in real time and make sure the plan looks good for your clients.
View the plan as any invited collaborator
Another way to see the plan as any of your invited clients/collaborators is to copy their invite link and open it in an incognito browser to view the project as them.
Please Note: if you do this, you will still be able to make changes/complete tasks/do anything that your client is able to do in the plan. If you make a lot of changes while viewing the plan as that collaborator, the Activity Feed with show all of those actions as completed by that client. It could lead to confusion, so be careful using this method. This is why I recommend inviting your personal email as a test collaborator.
Select a Collaborator that is NOT a Licensed User to bring up the collaborator info modal
In the collaborator modal, click on the Copy Invite Link located towards the top right corner of the modal.
Open a new/incognito browser and paste that link. You will see the plan as if you were logged in as that client. You will notice at the top, the navigation bar is different - this removes all permissions you have as a user.