There’s an interesting discussion in WooCommerce Issue #2571. regarding the default state of the “Deliver to a different address” checkbox.

For a less cluttered checkout screen and from a UX view point, we could uncheck it by default

 

Add this code to your functions.php

add_filter( 'woocommerce_ship_to_different_address_checked', '__return_false' );

Or to enable it by default add this code to your functions.php

add_filter( 'woocommerce_ship_to_different_address_checked', '__return_true' );