If you are taking photos using long exposure times, and the camera is on a tripod, the action of pressing the shutter button can cause the camera to move slightly. Depending on the exposure time and subject this may cause the picture to become blurred.
The Ideal solution is to use a remote shutter control such as the DMW-RSL1.
However, if you do not have one of these or forget to take it with you, you could use the self timer mode. Usually 2 seconds is enough to let the camera settle after pressing the shutter button.