Which file? In the vast majority of cases, this method will identify all files associated with an app. If you have difficulty deleting one, that's a different issue.
Yes, you can just drop the .app file in the trash in most cases. It's not necessary to use this method, unless you want to fully delete all files/folders related to an app. In most cases those files/folders only take up space and won't affect performance. In some cases, there are processes, Menu Bar items, etc. that won't go away unless you use this method to fully delete all the related components of an app.