As a search engein it combs through a great many job posting sites and lets you know when they posted. They can show you hiring & salary trends and let you aearch in other cities. Plus you can have new postings sent to you automaticaly. You can also see who made the posting if you want to avoid hiring agents.
But! They are not an actual job posting site, more like a third party search site. They just direct you to the site which has the posting for the position that you are looking for. So you will have to register with the other sites that you are sent to.
Yet with how nicely it will streamline your search I feel it's totally worth registering with other sites.