Explanation
This licensing will be required for the Field Service Schedule Optimization user, as it allows accessing Salesforce features and functionality such as optimization jobs and settings. References:
https://help.salesforce.com/s/articleView?id=sf.fs_permission_sets.htm&type=5

Skills are records that define specific abilities orqualifications that service resources have[158].Skill Levels are fields on the skill object that indicate the proficiency or experience of a service resource in a skill[159].
Assigning Contractor 1 and 2 different Skill Levels for repair Work Type would allow Universal Containers to configure the Contractors' experience by setting up criteria such as skill name equals repair and skill level equals high for Contractor 1 and low for Contractor 2. Assigning Contractor 1 as a Preferred Resource would not configure the Contractors' experience. Preferred Resources are optimization criteria that prioritize assigning service appointments to resources who have previously completed similar work orders or who are preferred by customers[160]. Assigning Contractor 1 and2 different capacities for repair work would not configure the Contractors' experience. Capacities are fields on the service resource object that indicate the number of hours available for work per day or week[161]. Assigning Contractor 2 as an Excluded Resource would not configure the Contractors' experience. Excluded Resources are optimization criteria that prevent assigning service appointments to resources who are explicitly excluded by customers or dispatchers[162].
References: https://help.salesforce.com/s/articleView?id=sf.fs_skills_overview.htm&type=5 https://developer.
salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_objects_skill_skilllevel.htm https://help.salesforce.
com/s/articleView?id=sf.fs_scheduling_policies_optimization_criteria_preferred_resources.htm&type=5
https://developer.salesforce.com/docs/atlas.en-us.api.meta/api
/sforce_api_objects_serviceresource_capacityhoursperday.htmhttps://help.salesforce.com/s/articleView?id=sf.
fs_scheduling_policies_optimization_criteria_excluded_resources.htm&type=5