Lot's of times your out of stock items are still bringing in SEO traffic so you want to keep them in your shop. If you have a large store, and products go in and out of stock all the time, it can be a UX nightmare for customers to constantly get shown out-of-stock products in their searches.

The fix is to move the out-of-stock products to the end of the loop, with this custom snippet in your functions.php. We're using this exlusively on Wine N Liquor which has over 15,000 products on the store and hourly stock updates.

add_filter( 'woocommerce_get_catalog_ordering_args', 'seanaus120_first_sort_by_stock_amount', 9999 );

function seanaus120_first_sort_by_stock_amount( $args ) {
   $args['orderby'] = 'meta_value';
   $args['order'] = 'ASC';
   $args['meta_key'] = '_stock_status';
   return $args;
}

Currently in use at:
Wild Posting
Gorilla Printing
Wine N Liquor
Wheatpaste Posters
Wheatpaste Posters
Poster Printing
Poster Printing NYC
OOH Marketing
Million Dollar Club
Gift Ideas
Dark Fibre
Hybrid Fibre-Coaxial
Window Advertising
Window Graphics
Window Wraps
Window Stickers