Sometimes writers like to start sentences with "and" or "but." I covered "but" in another post, and much of the same applies to starting a sentence with "and."
The mama cat licked her kittens. And they were dirty.
The mama cat licked her kittens and they were dirty.
There's a difference. The first implies they were really dirty, in a way. The second combines the two sentences for one complete sentence.
Starting a sentence with "and" is stylistic. I advise writers not to do it too much or it doesn't have the same impact as it would if it were used occasionally.