The example you've chosen just happens to be a molecule with a delocalised set of electrons - acrolein to argue that bonding electrons are always "spread all over the molecule".
You're another poster who confuses illustration of a concept, with the theory behind it.
If you wanted to walk around a city and see the sights, you'd want a street map that simply had the names of streets on it, and the main attractions. If you're driving through a city, your satnav needs a map that tells it which roads it can use and what the speed limits are.
Molecular orbital theory describes the map makers. The hybrid orbital model is one such "map". HOMO, LUMO is part of another. It's all QM, but you don't crack out the Wave Equation whenever you want to determine chemical behaviour any more than you would navigate on foot around a town using a list of GPS coords.