In general, yes. You will see a slight reduction in memory performance when using an IGP, due to the memory bandwidth being used to refresh the display. For a given resolution, the impact on memory performance has gone down over time due to the steady increase in overall available memory bandwidth.
Server motherboards typically have a dedicated frame buffer for their onboard graphics, and are therefore unaffected by this issue.
A (very) small number of AMD desktop motherboards implement a feature called "SidePort" which is essentially a dedicated IGP frame buffer. All the ones I've seen have been 128MB... if you need more than 128MB VRAM it starts using system RAM just like a normal IGP.
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