Banner carousels are everywhere. Do you remember the last time you saw a website that didn't have a carousel slider in homepage. Or do you remember seeing a carousel?
First of all image carousels usualy contain large images - so they contribute at slowing down your site.
They also push down other important content and usually have responsive / usability issues (mainly with scaling down on smaller screens).
With all those disadvantages it seems that everyone uses them. Have a look on themeforest - is there a theme without a slider / carousel on the homnepage? But is anyone looking at them or just scrolls down for the real content?