"wait for previous action to complete" is only intended to work with asynchronous actions of certain plugins, like AJAX, Local Storage, Pathfinding. (look for the clock icon on the event sheet). It basically replaces "On completed" event. It won't help you with other things.
Local Storage actions can easily take longer time on a slow device, or if you are saving/loading a lot of data etc. AJAX Request can take several seconds when you are requesting a file from the internet. Pathfinging Find Path can be quite slow on a large map, and so on. So yeah, never use "Wait 0.1s" with asynchronous events.