You will usually get a much bigger spark when you unplug a device (particularly a motor or something with large 'wound components'). This is because of the inductance which induces a high voltage, briefly, as the current reduces quickly. These sparks are a real nuisance as they can produce erosion of switch contacts and can be reduced using capacitors or diodes (in DC circuits).
namannitant. When you get your sparks from a plug it may well be because you start by making a brief contact and then break it.