Without a good foundation for a system, it will eventually run into issues related to maintainability, supportability, or performance. Finding the right balance of performance and capability versus cost is an important first step. Not every web site needs to have a dozen redundant servers powering it, but some sites might eventually need that capability. If the application is not designed to expand, you may end up having to rewrite it entirely.
Even if we're not engaged to build your system, we can review the plans your developer has for your system to give you a second opinion on the plan in question. We can help ask the questions you might not have thought to ask your developer before getting started.