In Desktop systems, the BIOS, by default, will disable the processor's graphics engine if it detects that an add-in graphics card is present. If the engine is disabled this way, it will typically also be hidden from the O/S (Windows, Linux, etc.). It is possible, however, to changes the BIOS Configuration such that the processor's graphics engine is always enabled (i.e. regardless of whether an add-in graphics card is present).
Ok, I've told you what to do if you want the processor's graphics engine to always be enabled, but you have to ask whether you should actually do this. The answer is normally No, as reasons for needing the engine enabled are few. The most common reason is so that you can utilize more monitors than the two/three that the add-in Desktop Graphics Card supports. There may also be cases where you need to do this in order to enable support for DRM within the chipset (Intel Management Engine), but this is typically not necessary as many add-in Desktop graphics cards provide this capability themselves.
Hope this helps,
...S
