Teachers have very little control over what students receive notifications for, or over the visibility of course content.
It is enormously helpful to be able to set materials to go "live" at a predetermined point in the future. But this requires those materials to be manually "published" in advance, and this results in students receiving notifications at a time that bears no resemblance to anything that actually affects them. This fills their inboxes with meaningless and confusing emails, and this, in turn, results in them not noticing, or not reading, the emails that are actually intended for them to read.
Likewise, the material set to go live later on is actually visible to them before that time. Though it remains locked, its visible presence, and any information conveyed by its title, may communicate to the students things that the teacher doesn't actually want them to know about yet (for instance, that there will be a pop quiz). The only way to avoid all this is to never set anything to go live automatically, and to instead manually publish the content at the right precise moment - which can be extremely inconvenient.
Canvas policy "puts notification decisions in the hands of the recipient," but it is often the teacher who needs to make that call. Provide teachers with more control over notifications so that they can save their students from pointless, time-wasting, distracting, confusing emails. And provide teachers with the ability to automate when materials actually become visible to the students.