According to several immunology journals, the improvement in recovery time was linked to the effect of hormonal balance on the immune system. A placebo effect would indicate that nothing whatsoever is actually happening, but there is strong evidence backing that hormones released due to stress significantly reduce recovery time by up to several days.
The placebo effect does not say nothing is happening, just that what's happening isn't link to external stimulus (active drugs in most cases).
If I give somebody a sugar pill (telling them it's medicine) or lay my hands on them pretending to heal them (if they believe in it) I'm doing exactly the same thing, I'm changing the mental state of the individual which can AT TIMES improve the body's own self healing mechanisms.
The fact that you can replace healing hands with sugar pills, ju-ju juice, magic cards or prayer pretty much indicates that it's the positive feeling in the mind.
The problem is, that many illnesses don't respond to the placebo effect (some do) & real medical intervention is required.
For that reason, placebos should only be given by qualified medical professions (as they are best armed to determine if a placebo would work) - but as they are not reliable (it does not work for pessimists that well for example) - they avoid it's use all-together.
It's not good medicine to give somebody sugar pills if they have a real condition which would be better treated by giving them real drugs with an active ingredient.
The other problem is the mind-set required to believe in all that hocus-pocus often expands to other areas - causing people to resort to nothing but placebos for serious illness or other detrimental life factors (instead of getting real medicine or actually resolving the problems).
Placebos can work for minor problems I agree, but it's bad medicine & indulging delusional thinking (which increases the propensity for mental illness).