Sterno is many things to many
people. It's basically a mix of
ethanol (the stuff in
beer,
wine,
vodka) and
methanol (antifreeze).
If you're a wino (and not worried about going blind or dying) you can drink the stuff. The problem is that your liver takes methanol and turns it into formic acid and formaldehyde (yes, the stuff used to embalm cadavers). Having this stuff in your blood stream causes all sorts of nastiness, mainly death. The benefit of drinking sterno is that the ethanol distracts the enzymes responsible for alcohol breakdown long enough to allow the methanol to dissipate, thereby reducing the amount of methanol by-products that make it into your system - in fact, ingestion of ethanol is the preferred treatment for methanol poisoning.
So why go to all the bother of drinking it? Well, just like other recreational alcohol concoctions, it produces a high. Drinking it once or twice won't likely produce lasting damage to your body, but continued exposure will result in blindness and eventually death.
A nifty example of Sterno's effects is the old man in The Andromeda Strain. A long time abuser, he showed symptoms of acidosis, irritability, weakness, etc.
On the good side of Sterno, it makes great camping fuel for cooking and heating...
But I digress.