Talking about the Intel ones, disable igfxtray as what malbky said, also persistence module if you have not opened the configuration of the display using Intel's app. If you have changed some settings in it (let's say contrast level), the settings will not be automatically applied each startup, you have to launch persistence module manually to get the changes back.
I have no idea about hkcmd, but I used to disable it always. I did not face any problem.
EDIT: hkcmd is for changing Display settings by using keyboard shortcuts. You can assign them by going to the Intel display settings. Disable it if not needed. Also if you disabled persistence module there is no need for this. But changing brightness from power options (or by the keyboard shortcut like Fn + F6 just for example, differs from a PC to another) has nothing to do with hkcmd.
Confusing explanation, sorry.
