Having dual monitors allows you to open programs on different screens. This is a very efficient solution when the user constantly needs to “alt-tab” between programs. Open one program and drag it to the second screen, then open the next on the main screen is the process.
There are some programs, typically industry specific types that deactivate the min/max and x features in the upper right corner, (the middle and end buttons). Without the ability to reduce the window without closing the program prevents the user from moving the window to the second screen. This effectively renders the second monitor useless.
The solution is a simple keyboard combination that will move the window back and forth between screens. Hold down the window key, Shift and left arrow, to move one direction and the right arrow to move the opposite direction.