In a 700cc cycling wheels, the number of crossings depends very much on the number of spokes. As a rule of thumb, the maximum number of crossings = Number of holes(spokes) / 9. Therefore, if we build wheel with a 28 holes or 32 holes hub, the maximum number of crossing is 3, and with a 20 holes or 24 holes hub, the maximum is 2.
In theory, a wheel should laced with as many crosses as possible in order to reduce the lagging cycle due to torques/power transfer. The closer the spokes are tangential to the hub, the better. However, in real practice, if we try to use 3 crosses on a 24 holes hub, the spokes will certainly run into the head of the next spoke.
A benefit of fewer crosses is that the length of spokes will become shorter which makes makes the effective bracing angle greater.