I am planning to use my Laptop as desktop and buy another new laptop because of various problem my laptop is creating like battery, its display is also creating problem. I want to use atleast two monitors at once with my laptop but problem is it has only 1 vga port and current laptop display is not working properly. So at most I can only attach 1 Monitor to it since its main display is now faulty. What if I remove its display completely and use only its hardware part as desktop and attach another USB display device to it ?Now my question is how useful will be usb display device, are the practical and can use regular day to day stuff ?

USB display adapter or USB display graphic cards can't replace the normal display panel in laptop because it is not possible to have such bandwidth which is required to make a good display available through USB, even in USB 3.0, the bandwidth a proper VGA display need is not there. So in my suggestion, if you need for some emergency or occasional use then it is ok but for day to day life, they are impractical and next to useless.