It would be very helpful to have Text on the settings page that indicates that checking the sync box will increase the size of the feature class with every edit made and that the increased size will impact your credits. This type of text exists for the Layer Optimization Setting. I believe any setting that will increase the size of the Feature Service should should have text indicating this. There is no other obvious way for people to know that the size of the feature service will increase over time. This type of increase can end up costing an organization a lot of credits for no reason.