You don't have to pay a fee to use this program. You can apply for free.
You can join the Adsense program very easy. After you are accepted into the program you just have to paste a bit of code into your pages.
Because of their method to identify what a page is all about you don't have to spend time finding advertisers, they will place on your page the exact advertisers you need.
If you own a really big network of sites, you don't have to apply for each of them. Just apply once and use the same code on every site.
And many other benefits but let's take a look at the disadvantages too:
The biggest disadvantage that most users report is that the stats Google supplies are inadequate. Even if they're very easy to understand they don't tell you which ads people are clicking on, or which keywords are involved. That's very frustrating.
The minimum payout is $100, users that have sites which don't receive much traffic say that it's too high. If you plan on doing from adsense a successful business. don't worry about this.
If you want to display ad sense ads you may not display other text based ads on the same page with them. When you apply humans will check your site for approval, if you are rejected just try to understand why they did, fix it and appeal again.
You will never know how much from the amount that advertisers pay you will receive. You will just receive an unknown percentage from that amount.
With this benefits and disadvantages in mind you can now start to learn all the inside secrets of adsense and develop a real online business. You can start doing so by reading about it on major make money online forums, tring to understand all there's about it many users discuss this topic very deep.