But when using a waterfall model for a project that can hardly be called suitable for it, the following disadvantages appear:
the integration of all the results obtained occurs suddenly at the final stage of the model. As a result of this single pass through the entire process, integration problems tend to be revealed too late. Consequently, previously undetected errors or design flaws will appear, increase the degree of risk with a small task of time to restore the product, more info at
https://www.mindk.com/blog/web-application-development-cost/
the client hardly has the opportunity to familiarize himself with the system in advance; this happens only at the very end of the life cycle. The client is not able to take advantage of the available interim results, and user feedback cannot be passed back to the developers. Since the finished product is not available until the end of the process, the user takes part in the development process only at the very beginning - when collecting requirements, and at the end - during acceptance tests;