Correct geometry would be the why you could use them or not. Drawbacks are strength and ratio accuracy. The up side is simplicity.
On my SpeedMaster heads with different valves and springs that they come assembled with (I bought mine bare) I ended up using Hughes Rockers. I think I need a thin shim under the stand to dial them in, but that was with my valve heights, cam lift, block deck height and square, gasket thickness and rocker stands to start with.