For someone like me, earning to help pay my bills from my back list being the most important. ;) Books that were no longer being pushed by a publisher can find new audiences when re-released, so if you have an option to try it, why not. But there are many other great reasons I admire independent publishing too.
It's creativity unleashed. I've been involved with publishing long enough to know that there are far too many great writers for the traditional publishing slots available, and that's the sad truth of it. When I hear an excited, keen author saying they want to write for X line, (where they'd obviously be a great fit and they have the talent to do so) I'm forced to look at how many books that line publishes a year, and how many of those might be repackaged books being put out for a second time. The maths can be very dispiriting indeed.
Another crucial aspect where self publishing is changing things is making books available that might not otherwise find a publisher because they are risky for a publisher -- edgy fiction, taboo sexuality, political or social books with controversial subject matter.
Here are just a couple of indie projects that show what can be achieved. First up, The Almond Tree, and secondly Excessica (who published some of my books before I was able to take on the task for myself) You can click on the graphics to find out more.