Themes
Say what it encloses
An orbital picture is a contour at a level somebody chose, and almost no source says which. Every one here is drawn at a level found by integrating the density, and states the fraction it encloses.
Exactly zero
Where symmetry forbids an interaction the overlap is not small, it is zero. Computing it and finding arithmetic noise is a different kind of statement from computing it and finding a small number.
A basis is not a thing
Hybrid orbitals, localised bonds and canonical molecular orbitals are related by transformations that leave every observable unchanged. Arguing about which is real is arguing about a coordinate system.
Symmetry settles it
Whether a molecule can have a dipole, or be chiral, or show a particular spectral line, follows from its point group alone — with no reference to what the bonds are made of.
One electron only
Every orbital drawn here is a hydrogen-like solution. A many-electron atom has no exact orbitals at all, and keeping that in view is the difference between a model and a picture of reality.
Taught confidently, and wrong
This subject has an unusual number of explanations that are memorable, widespread and false. Each is stated fairly here and then tested against a computation rather than an opinion.
Counted, not quoted
Node counts, bond angles, overlap integrals and point groups are all computed while the figure is drawn. None of them is a number recalled from a table.