[kazinator]

Configurable notifications (on/off) with opt-in workflow when the user installs the application or joins the site or whatever are probably the good all-round solution. Users who hate notifications don't opt in, and all is good.

Users want notifications that are pertinent to them and useful. Usually that means notifications which are triggered by the activities of other people. Apps that generate internal notifications just to remind the user of their existence("you have not used me for a while" kind of thing) are obnoxious.