One of the great features of SharePoint 2013 is User License Enforcement. This enables you to map users, or Active Directory security groups to a SharePoint license level.
User License Enforcement is disabled by default and is dependent on Claims authentication. However, Claims authentication is the default in SharePoint 2013 http://technet.microsoft.com/en-us/library/cc262350.aspx.
To enable User License Enforcement, open the SharePoint 2013 Management Shell and type Enable-SPUserLicensing. To confirm User Licensing is enabled type Get-SPUserLicensing. Enabled, True should be the output if it’s enabled.
To map an Active Directory security group to a SharePoint Enterprise license enter
$a = New-SPUserLicenseMapping -SecurityGroup “yoursecuritygroup” -License Enterprise
Add-SPUserLicenseMapping $a
Replace Enterprise with either “Standard”, “Project”, “DUET”, or “WAC” depending on the license level you wish to enable. Project is for Office Project Server, DUET is for SAP and WAC is for edit rights in Office Web Apps.
In the screenshot below I’ve mapped two Active Directory security groups to different license levels, one to an Enterprise license and one to a Standard license.
Once you have configured the license mapping, enter Get-SPUserLicenseMapping to view the mappings.
Once the User License Enforcement has been configured users will see a different view dependent on their license level. Below you can see a user mapped to an Enterprise license can create sites, such as Business Intelligence Center.
The user in the screenshot below is mapped to a Standard license and has a different set of site creation options.
If a user with a Standard license accesses a page containing an Enterprise level web part they may see an error relating to a lack of license.
For a full list of licensing PowerShell cmdlets visit the TechNet site http://technet.microsoft.com/en-us/library/jj219609.aspx
Richard Skinner 
How can we have a standard licensed web application and an enterprise licensed web application on the same farm when OWA only excludes excel files at the farm level instead of the web app level? What experience do the standard licensed users get? Can they still use OWA for Excel?
With OWA, you have to exclude OWA from managing excel files so that excel services can handle the excel files and this is a farm wide setting in OWA instead of a per Web Application setting. Question, what happens when a standard license mapped user clicks on an excel file?