zohaa

Several reasons. If you lose barracks/hon and WF/Air then its all you really have for defense. It also helps distract the other team for 10-20 seconds. If you've been placing fakes every two - three minutes for about 15 minutes, they'll automatically assume fake, so when you place a real one, chances are, they wont look very hard. If they have the field, a fake can sometimes help them retreat a little bit, allowing your team to push forward.