Bringing ideas to life early in the project helps us to narrow and validate requirements with real users in a controlled lab environment, before a line of code has been written.
Testing early in the design process will ensure ideas/concepts are logical and easy to understand. Receiving feedback in this early stage allows for changes to be made quickly - there is also the opportunity to test a variety of ideas in a short period
Testing early in the design process will help avoid pitfalls further down the line. This is one of the most valuable parts of usability testing; determining and resolving issues early in the design process is quicker and cheaper than redesigning work
that has already been built.