Hey Simon,
Glad to hear from you. I think ROman gave an excellent example. It is from the broker, indeed.
When the brokers buy MetaTrader to offer it to the clients that have some access to the backend, this means they do different settings.
It is about you fining how much your broker can handle.
Anyway, stay below the limit, because you do not want to miss nice trades just because you overloaded it.
Cheers,