I would have thought heat conduction into the board was desired.
Yes, it can be, and sometimes components are just elevated only enough to clear the PCB and are supported by their own leads with no standoffs. This can be fine for something like a TV where the only physical stresses components will ever see is while in infrequent transport.
Other equipment must be more physically robust and hence standoffs are then often used.
IME standoffs are more often seen in old equipment with Phenolic PCB's that are more susceptable to elevated temperatures.
I have seen quite tall standoffs used with other components below, right on the PCB so standoffs can also be used to help with density/routing paths.
Other than power resistors (some with integral pressed metal standoff leads) it is not so common to see hollow standoffs these days with designers more conscious of better efficiencies in modern appliances/equipment and also the more commonly used FR4 having better heat tolerance.