Building your own team delivers the deepest product knowledge. The people internalise the business domain over time, and this context remains with you. The cost shows up as a long ramp-up and fixed costs: recruiting a strong engineer takes months, onboarding adds more time, and the payroll continues regardless of workload.
Full outsourcing is the arrangement where the vendor owns delivery: they staff the team, the partner manages the day-to-day work, and they absorb the delivery risk. This fits well when the scope is reasonably clear and there is someone who can make decisions quickly. It breaks down when nobody on your side owns the product, as a vendor will not guess what the business wants.
Hiring individual contractors sits between the two: you add engineers but keep the planning and the management in-house. The main advantage is speed — a suitable engineer can start almost immediately — and it scales down as easily as it scales up. The condition remains that your own leads have to have the capacity to direct the work. Without that, you end up paying hourly for uncoordinated work.
Most of the time, companies blend them. A frequent arrangement keeps the critical decisions and the core system in-house, while a partner covers peaks, well-defined modules or platform work. The principle holds: retain what differentiates you, and delegate what is well understood.
Three questions usually settle it. To begin with: hire react navigation developer is the system the product itself, hire senior node.js engineer or a cost centre? Second: how long does the work continue — months or years? Last: who owns it once the vendor leaves? Answer these three honestly and the appropriate option usually chooses itself.