On iOS Scheduled Summaries are really great. That's become my personal default on my phone. Scheduled Summaries roughly every 4 hours during waking hours and the default choice every time the question pops up for a new app is "In Scheduled Summary". I could see with some modest UX improvements Scheduled Summaries becoming the default for more people.

Heavy use of Scheduled Summaries does also lead to me wondering why there isn't a "default notifications to Ask/On/Scheduled Summaries/Off" global setting, though I would want that choice between Scheduled and Off at least.