Does disabling the integrated GPU make any difference if I have a graphics card?

If the integrated GPU isn't doing any work, I wouldn't expect a noticeable change in performance or temperature just from disabling it. The power difference may be small too, though the exact behavior depends on the CPU and system.

For a desktop that's working normally, leaving it enabled is a reasonable default. You can always test both settings if you're curious.

I would leave it on as a backup display option. If the dedicated card has a problem, integrated graphics can help with troubleshooting, provided the motherboard has a suitable display output.

If you disable it in firmware, you may need to change that setting or reset the firmware before you can use it again. Don't count on it automatically switching back on.

Disabling it can be useful when software keeps picking the wrong GPU, or when you don't want another graphics device and its drivers showing up. Check the app's GPU selection and where the monitor cable is connected first.

There are reports of unusual game performance differences even when the dedicated card appears to be in use, but the cause isn't clear. If you see that, compare the same game and settings with the integrated GPU enabled and disabled rather than assuming either setting is faster.

There may be a small memory benefit if the system reserves RAM for integrated graphics. Whether disabling it gives that memory back, and how much, depends on the firmware configuration. It's probably not a compelling reason unless you're tight on RAM.