You do not need to allocate an Email to Case Premium license for the packaged Case Presentation Layer to every user in your Org; however, each user that intends to interact with the Case Presentation Layer application will require a license.

Please note that as of version 5.0 of Email to Case Premium (December 2017), Case Presentation Layer is now included as a packaged component in Email to Case Premium and no longer offered separately. If you are an existing user of Case Presentation Layer, please refer to the following documentation (at the bottom) as well as special considerations for optimizing the Lightning Experience with Email to Case Premium.

Each user that would like to use Case Presentation Layer will require a license for Email to Case Premium.

The Case Presentation Layer packaged component can replace the Case Comments related list on your case page layouts.

If you are using an older version of Case Presentation Layer that is separately licensed from Email to Case Premium, you may continue to use the existing component. However, as issues arise from Salesforce platform updates, the resolution will often be that you update to the latest packaged component.

If you have unlicensed users that need to view Case Comments, you should do one of the following:

• Leave the Case Comments Related List on the case page layouts; or,
• Create separate profiles and layouts for users with and without access to the Case Presentation Layer through Email to Case Premium.

Note: Users that do not view Case Comments through the Case Presentation Layer, for example, do not need licenses.

For more information, see "Assigning Licenses for Installed Packages" by clicking on Help & Training at the top of your Salesforce.com account or contact presentationlayer@internetcreations.com.