Scanreg is used to check the registry on boot to be sure it is not corrupted. It runs once, then unloads, so you don't have it running during normal usage.
Systray doesn't need to load for the most part, however if you use the normal Windows Volume Control, it will not be able to appear in your system tray if systray.exe isn't running.
Loadpowerprofile will put itself back if you disable it. I believe it's related to ACPI functions, all it does is set up the profile for power management.
pointer.exe would be the Intellimouse software. If you want the mouse to work properly (like the wheel doing what you want it to and being able to modify settings) then don't unload it or disable it.