When using Alfred to launch application, those apps does not always have their main window opened in the display on which Alfred was shown. This is confusing, you're using alfred in one display, and its action occurs in another display. It would be better if all visual feedback occured in the same display.
Since mavericks, all screens have a main menu bar, and can be the primary display depending on current active window. One of the consequences of this behavior is that applications have their main window opened in current primary screen. Currently Alfred is always shown on the same display, whatever the current primary screen is.
The problem is that you generally expect to have Alfred's actions being done in the same display. Worse, if you wanted an application to open in the same display than Alfred, you can easily forget to check what is the current primary display, and then discover that the application has been opened in the wrond display once it's too late.
A good workflow IMO would be to always show Alfred's window on current primary screen, and give the users the oportunity to change the primary screen and let him hide it, changing active window, and re-open it before doing any search.