Today is about getting discovered. One way is to publish your book in different formats. What do I mean? There are 3 that I know about: audiobook, paperbook and ebook.
For those of you who write for children, paperbook is probably the only version to do, esp if you write for younger readers eg under 9 year-olds. I currently write for 7-9s and will only publish in print for that age range, especially that I have discovered children of that age do like paper books more. When I come to write the next series, which will be for 9-12s, I might do an ebook version, too. Children of that age do have Kindles as I have been told by one mother who wanted a book for her daughter who was ten. My previous children's books are only available in ebooks for now, but I plan to start putting them back into print this year.
For those of you who write for adults, all three choices are good options, esp ebook and print. There is also audio. I won't be doing this as I don't make enough money on my adult ebooks to warrant this.
I believe the more formats you have out there, the more readers you can reach. I do like to have print copies of my books to hand, esp if I go to a meeting or a library where I can meet people and show them my book. I might sell a copy or two.
So, if you write for older children, think about publishing your book in print and digital. If you write for adults, think about publishing your book in all three formats.