Votes. Those little stars which can be EXTREMELY difficult to get. While most people focus on reads, votes are equally important.

A vote shows that a reader likes your chapter enough to press a little star- it's like if someone likes your photo on Instagram or Facebook.

The amount of votes you have on your book is an indicator of how many people like your book. Anyone can get reads if someone so much as clicks that read button, it doesn't matter if their book is crap. Someone can have 1k reads but they are just on the first chapter and then everyone clicked off the book. 

If you have votes, it shows that people are enjoying the book. Some readers will look to votes on more popular books as its an indicator of how good the book is (people don't tend to do this with smaller books because it's unfair).

Votes also increase your chance of being ranked which we've already talked about.

Votes also can tell you who your readers are and you can message them and befriend them- this can help you make more friends on Wattpad.