That's more to do with how you setup to trigger the commands.

Async here really means that it doesn't block with your typing, jumping around in the text editor if plugin starts doing some heavy work in the background due to some action that got triggered by whatever event you had setup for plugin to do. One of the plugin that I particularly remember was syntastic (I haven't kept up with it to know if they've fixed this or not) that would just create janks every now and then if the workload was heavy.