My opinion as a cyclist is that I should basically only be using my bell on pedestrians when the pedestrians are wandering onto the bike lane. If im cycling through a shared space, I find it extremely rude to ring the bell, because it feels like I'm telling people to get out of my way, but they have just as much right to a shared path as I do. Some cyclists ring their bells because they're worried a pedestrian might suddenly turn into their path, but I think if one is concerned about that, it's a sign youre cycling too fast, and should just slow down.
With cars, I will sometimes proactively ring my bell at them if I think they're not sufficiently aware enough of me though.