When I was still working in Pax handling at TXL
(Berlin, Germay) we had a funny case:
Some employee found an unattended bag in the terminal. He called the border police, who after nobody answered the call, called a bomb squad.
The armourer used an explosives detector, which showed signs of explosives, so they used a water gun (essentialy a piece of pipe on a tripod filled with an explosive charge and water aimed at the suspicious object, the high velocity water jet is supposed to take a bomb apart before it has time to explode). A few minutes after the explosion a Russian gentleman appeared and complained that they just blew up several thousand bucks worth of electronic test equipment while he was having a leak. Apparently some fumes from the gear gave a false positive explosives indication on the explosives detector.
Another reason for keeping close to your bags: There are plenty of thieves and pickpockets around in public places like airports.