An in-house team delivers long-term retention of knowledge. The developers absorb your customers and your data model over months and years, and this context remains with you. The price is slow hiring and fixed overhead: recruiting a strong engineer routinely takes several months, ramping up adds more time, and the cost continues through the quiet quarters.
Full outsourcing implies an external team owns the outcome: the partner staffs the project, the partner manages the day-to-day work, and they carry the risk of missing the date. The model works when the scope is reasonably clear and you have someone who can make decisions quickly. It fails when there is no one to answer questions, since a vendor cannot invent your business rules.
Team extension is the middle option: you add engineers but keep the planning and the management on your side. The main advantage is speed — a suitable engineer can start far sooner than a new hire backend developers — and it scales down as easily as it scales up. The trade-off remains that your technical leaders must have the capacity to direct the work. Without strong internal leadership, you are paying hourly for uncoordinated work.
In the real world, the models mix. A common pattern puts the architecture and the core domain inside the custom software development company, while an outside vendor handles discrete features, migrations or mobile clients. The line holds: retain what differentiates you, and outsource what is well understood.
Three questions usually settle it. To begin with: is this php software development company the product itself, nodejs consulting services or a supporting tool? Second: over what horizon will the work last — one project or a permanent roadmap? Third: who will maintain it in two years? Work through them with real answers and the right arrangement becomes obvious.