Building your own team gives you the most control. The developers internalise your customers and your data model over months and years, and this context sits inside the company. The cost comes in the form of a long ramp-up and fixed costs: recruiting a strong engineer takes months, getting someone productive adds more time, and the payroll carries on whether the roadmap is full or empty.
Handing a project to a vendor is the arrangement where an external team owns the outcome: the partner staffs the roles, the partner manages the day-to-day work, and they absorb the risk of missing the date. This fits well when the outcome can be described and you have someone who can make decisions quickly. It works badly when there is no one to answer questions, as a vendor cannot guess what the business wants.
Staff augmentation sits between the two: you rent capacity but keep the management in-house. It is fast — the right specialist can join almost immediately — and the commitment ends when the work does. The condition is that your own leads have to have the capacity to direct the work. Without strong internal leadership, you are paying for effort with no owner.
In the real world, companies blend them. One durable pattern puts the architecture and the core domain inside the education software development company, typescript development company while a partner handles discrete features, migrations or mobile clients. The principle is simple enough: keep what defines your product, and contract out anything a competent team can specify and deliver.
A few questions usually settle it. To begin with: is the system central to how you make money, or a cost centre? Then: how long will you need this capacity — months or years? Finally: who owns it once the vendor leaves? Work through them with real answers and the right arrangement becomes obvious.