With the screw all the way in, it needs less vacuum for the amount of advance supplied.
Each engine is going to want or need a different amount of advance. If your engine only pulls 8" of vacuum at idle then you would not want to hook this can up to full manifold vacuum because it would dither in and out and make it hard to get a steady idle. However, on ported vacuum it would probably work well because I imagine you could pull around 14" a light load. For instance, I ran ported vacuum to mine as it pulled around 11" at idle but 16-17" at light load going down the road. Mine ran best with around two turns out which if you look at that chart means it needed 14.6" of vacuum for full 22 degrees of advance. As you open the throttle and put more load on the engine, vacuum will decrease and the vacuum advance will decrease with it.
I can't say what every setup will like but mine ran well with ported vacuum advance and 16 degrees of initial timing. I think the standard amount of total advance (mechanical plus vacuum) that most street small blocks will tolerate at light load is somewhere around 50-54 degrees.
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
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'69 Camaro Beater-SFT 327-M20-Moser 4.10-sold
'02 Z/28 vert-stock-sold and totaled