The cross uses much less screen space and computing time. Moreover, when atoms are bonded, crosses are not represented at all, and atoms are identified just by the ends of the bond lines, decreasing even further computation needs. However, wired objects do not have a 3D representation, so diffuse and specular lights are not reflected, becoming poorly visible when using lights, unless the ambient component is important, about (0.5, 0.5, 0.5).
In Solid mode, the default is to represent atoms as constant spheres (Variancy = 0.0 and Size = 0.8), slightly larger than the bonds (Size = 0.5). An elegant style is to represent atoms as constant spheres with the same Size as bonds (0.5).
To represent compact cristalline structures, atom Size and Variancy must be 1.0, to be consistent with cell dimensions. This style can also be used to represent molecules, in order to emphasize the atomic radius and electronic distribution. To change the default Size select Atom->Config.
Size x (Variancy x Radius + (1 - Variancy) x Min)where Radius is the atom radius and Min is the minimum radius, by default the H covalent radius (currently 0.37). To change this default select Atom->Config.
In Wired mode, Variancy is always 0.0 so all atom crosses have a constant size, given by Size x Min.
In Solid mode, when Variancy is 0.0 the atom spheres have all the same size, when Variancy is 1.0 the atom spheres are scaled directly by the atom radius.