Probably all of you have encountered Push Notifications. A lot of portals are bombarding us with requests to allow notifications as soon as we visit them. Despite this abuse, when used in responsible way, Push Notifications can be very useful. They key advantage is that web application doesn't have to check if the user is online or not, it can simply request delivery of push message and user will receive it as soon as possible. Of course this capability is not for free and I will try to show where the cost is hiding.