I am desigining a photo layout that will go accross 3 22X28 canvas. If I create 3 Art boards with 4 inch spacing in between each artboard, what would be the best way use graphics that go accross all 3 artboards but do not show the artwork in between the artboards? I thought about a clipping mask but not sure if I was going down the right path.
You could do that by duplicating the layer two times making the three clipping masks in place so they match then repositioning them within the art boards leave a little bleed in all cases where the image butt meet.
I would link the file in the first place in order to keep the file size to a minimum.
You clearly mention that you'll separate the arboards by four inches, and you don't want to see the artwork in those inter-spaces. So this fact about artboards will not apply in your case; rather it's useful to know when bleeding artwork across artboards generally:
If you abut artboards flush, then draw (or place) artwork across them, the correct artwork segments will appear on each artboard when printing or saving to PDF. The segments will align correctly in spreads. If you include bleed, the output (paper or PDF) will adjust correctly so that the artwork will align after trimming.
A nice feature for some types of work.