Imagine you have created 2 Scheduled transactions: one for your internet bill and one for your TV bill. Because those two transactions are due on the same day (let's say 7th of each month), you have created two Scheduled transactions in MoneyWiz: one dated 7th at noon for internet and one dated 7th at noon for TV.
Now, what will happen on 7th at noon?
if the aforementioned setting is disabled, you will get 2 separate push notifications on your device to notify you that those 2 transactions became due (you'll see the details of both),
if the aforementioned setting is enabled, you will get just 1 push notification, informing you that a total of 2 Scheduled transactions became due.
This means that this setting, if enabled, sends out just a single push notifications for Scheduled transactions that became due at the same time, no matter how many transactions became due. If you have many Scheduled transactions that become due on the same date and time, you might want to enable this setting to keep your Notifications list organized.