The web is a rather vertical place. You read a web site like you read a physical page: left to right, top to bottom. But sometimes, you want to step away from the verticality of it all and do something crazy: make a horizontal list. Or even crazier, a horizontal site!
By now, any article about carousels should come with the disclaimer: You may not need a carousel. Carousels are easily abused. Kyle Peatt has more details on the carousel controversy.
Part of the blame can be put on the user experience of carousel plugins themselves. Scrolling through a carousel is less satisfying and more awkward that simply scrolling down a page. Basically, you can't flick through them. Third-party libraries should at least be as useful as native behavior.