Advantages of using a subcontractor rather than an in house team
The sub-contractor will already have the specialist skills required so companies do not need to train current employees to learn these skills.
The sub-contractor already has the facilities available for manufacture so the company do not need to invest in new machinery or tooling to complete the work.
The work that needs done my only be a small part of the design or manufacture or only be needed for one product so hiring a sub-contractor can be more cost efficient for companies in these situations.
Advantages of using an in house team rather than a sub-contractor
Subcontractors can charge their own prices so are more likely to cost more than a current employee.
In house teams are employed by the company and so will be reliable to do as asked and complete the job; sub-contractors do not have the same loyalty to the company.