Without diamonds on the cushions I find it easier to judge using 2 than 1, to cannon an arbitrary ball on the table. Don't know if there's actually a physics reason for it though. You do want to be mindful that a full contact might move the object ball towards a pocket, rather than a safe spot.
Now if snookered behind a baulk color, pro's take a two cushion escape to clip the pack thin and the get cue ball back in baulk. Don't see how you can do that with 3 cushions.... see here: (
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Rolling into the pack of reds from the side (one cushion) or from the top cushion (black side) just depends on the spread and not leaving anything for your opponent, so that really depends on the situation.