Unlike dedicated graphics processors, the integrated GPUs in accelerated processor units don’t have their own memory bank, and so rely on your system memory. This means they use slightly more RAM than your standard independent hardware setup.
Exactly how much RAM an integrated GPU uses depends on the model, but for Intel, it’s often something to the tune of 64 - 128MB. It’s a pretty negligible amount, but that’s a big reason why they’re not so great for gaming.
Your typical AMD IGPU should use around 2GB of RAM, still not really all that much, but if you’re running a very basic 2 x 4GB RAM system, you can expect a minute dip in general system efficiency. Don’t let that put you off a quality APU, though. 2GB on beautiful graphics is RAM well spent!