In Australia bells on bikes are mandatory. I think that makes good sense. Need convincing? Here are some good reasons for bells on bikes.
“Here I come!” A bell is a handy way to warn other path users of your approach. It avoids the “whoosh” surprise factor of having a cyclist “appear from nowhere” and frighten the life out of them. If you give enough warning you can also avoid those moments where you both move in the same direction instead of making way for each other.
“Wait for me”. Cycling with your kids or friends is a friendly activity. That means not accidentally leaving anyone behind. A bell can help with that by appealing “wait for me!”
“Look at that”. It would be a pity for the others in your group to miss some of the sights you’ve spotted, a bell can help call attention.
“Watch out for that”. A bell and some exaggerated gesturing can help warn your fellow riders of hazards like drains, glass, sand, etc
Choosing a bell. Some bells sound friendly. Others sound grouchy. Try it out and choose one that suits. I find ringing ones with a sliding lever and internal cog type mechanism last longer than the spring and ping type.