Normally, writing in the console is an expensive operation in terms of performance. However, this is not the main reason for recommending
to disable the Console plugin in release builds. The reason is that, due to the nature of hybrid applications, users can easily observe all of the printed in the console content. And this is something you would like to avoid (at least in most of the cases).
However, excluding the Console plugin for published apps is far from mandatory and you are (and will be) able to include it in official (release) AppBuilder builds.
I hope this helps.