Prototyping is a common practice in many disciplines. Everybody understands the benefits of trying a scale plane in a wind tunnel before building the real aircraft. It is better to check and correct the aerodynamics of a smaller-scale plane model than discovering any issue once the real one is built and in flight. This is also true for apps.
Model of the supersonic transport in the NASA full-scale wind tunnel in 1973 (Source: https://commons.wikimedia.org/wiki/File:SST_model_in_Wind_Tunnel.jpeg)
A prototype may look similar to a real product, but they are very different in nature. A prototype does not have to work, it only has to look like it does. In addition, a prototype only tries to simulate a few aspects from those that the final product will have, in particular, those aspects the designer considers more important to learn about.
Prototyping...
