When cycling in the rain, they are the only sensible option. You can deploy them over the handlebars to keep your hands mostly dry (and the contents of your basket too, if you have one) - only downside is that puddles of water do gather between your body and the handlebars! They disburse water in great gouts periodically but it is mostly in ways that you can avoid being splashed by (for instance you can empty the puddle at the traffic lights when waiting).