What is the difference between plugins located in dependencies in package.json :

VS plugins in cordova { plugins{ plugin list }

What is the difference between plugins located in dependencies in package.json :

VS plugins in cordova { plugins{ plugin list }

Those should be identical in the best case.
Before Cordova used to not use npm and node_modules for plugins, but now it does. Before it had its own list of installed plugins in cordova->plugins, now it also uses the dependencies entry. A future version of Cordova will drop the dependencies completely.
Can this affect on my app performance, errors etc?
No.
The only thing that can happen is that some Cordova tooling is confused. But package.json should already win right now - which is one of the reasons why I always tell people to update their CLI tooling.
Thank you for the information sir! You’re always very helpfull 
Actually, this might all have been bullshit.
The plugin part of config.xml will be removed, but package.json will stay. cordova->plugins is for plugin configuration, like the usage description you are seeing there. So each Cordova plugin in dependencies should also have an entry in cordova-plugins.