There are two other ideas that exist already one that are by default set sums to off and another that is to set defaults by module.
Why limit to just as a whole product or module, why not give a default for builders or similar added to the Model Setting.
All models are set to default none for all summaries and line item type, then you the ability to set the default by module to whatever variation of sum or line item that works if it is different from the model (as line items are created they can start for example as boolean, all) and then the selected line item overwrites whatever the default option is.
This ties into several of my other submitted ideas, such as default coloring of text, and similar model scheme that can be applied for additional use cases.
