take a loot at the following picture:
Let's say that you would like to have two Acumatica instances connected to the same database. Is it possible? Definetely yes, just with pointing both of them to the same connection string and you'll get some kind of scalability.
But imagine that your Acumatica has execution of some automation schedules. How to make sure, that only one of them will be executor of Automation schedules, not both of them?
Very simple. Just add this key to web.config of Acumatica which should not be Automation schedules executor:
<add key="DisableScheduleProcessor" value="True"/>
Default value of DisableScheduleProcessor key is false, so you need to say which Acumatca instance shouldn't think about execution schedules. With this simple trick you can have two or even more instances of Acumatica and regulate which of those instances will execute schedules