It depend on what kind of fishes or corals. Lps can do well with moderate current or flow. Sps need stronger flow. Most fishes will do ok with flow like u find in a lps tank. But if u are keeping for example AT, they will prefer current like what u can find in a sps tank.
If u ask me, there is no fixed rule for current or flow. It all depends on your rocks scaping, kind of corals or fishes u keeping. These are all based on exp. As u gain more exp, u will know how to see. Reading off the net will only gain u the basics.