[Tomte]

But if the patent office doesn't accept your independent claim, one of the dependent claims must become a new independent claim, right?

So it's simply for the process of getting a patent (and some cost issues with registration)? After the patent has been granted they are truly unnecessary?

[fncypants]

You may have come up with what you think is a great new idea and several variations that are also useful. You claim the broadest one as an independent claim. And the refinements are dependent claims. The patent office may agree, and issues all claims.

If, later it turns out the big idea was not new, but the refinements are, then you may find yourself with an invalid independent claim but valid dependent claims (which are treated as though they stand on their own). Although you could have filed the dependent claim as independent just the same, it saves paper and cognitive time analyzing it, which is a good thing. And for that reason patent fees are more expensive if you add more independent claims rather than dependent.