Doesn’t interfere with page rendering
Doesn’t break stuff
However, that particular configuration doesn’t work for everyone. Despite taking precautions, there are some plugins and themes that won’t work even when the scripts are “deferred” with jQuery excluded. In addition, you could have problems with console errors, and weird messages like “Unexpected Identifier”, and so on.
Defer or Async?
Another consideration is that the “jQuery” script is one of the most popular and ubiquitous scripts in WordPress. It even comes bundled with the core installation. As a result, touching it in any way can be very dangerous, and will almost surely break your site – if not now, then in the future.
Everything “defer” except jQuery
Everything “async” except jQuery
Finding out which one is right for you is more a question of experimenting, than logic. It’s quite difficult to figure out which option you need in advance, because it’s almost impossible to figure out everything beforehand. Just when you think your site is working fine, you suddenly realize that some functionality is broken!
Whether or not it displays on Admin pages
Whether or not it’s enabled on checkout pages
The reason why there’s a separate option for checkout pages is two fold:
Your checkout pages are the bread and butter of your site. This is the last place you want something to go wrong!
Choosing One of Four Options With a Click
This allows you to experiment and see what’s working and what isn’t. Chances are that one of these is best for your site and you won’t need to do any additional configuration!
Plays well with Autoptimize