What is the point of using virtual machines, instead of ready-made assemblies a la OpenServer?

Question

open server

Good evening!
At the interview, the following question was asked: "What are you developing the site on?".
He answered that I use OpenServer, to which the interlocutors looked at each other and began to ask, what is it all about?
The question is:
- I still didn't understand from the conversation - is the use of OpenServer in development a bad form rule?
-- if yes, what should be used instead?

Answer 1

meaning in the maximum (or complete) approximation to the target (where it will be performed) environment.
otherwise, "funny" shnyags arise: like "everything works for me on Windows, deal with your penguin yourself" (and vice versa) or "wrote a mysql-request, locally everything is ok, but uploaded and does not work" (because locally strict mode is turned off, and on sale included) and all that.