Importance:
AWA
AWA explains how to stop and start campaigns.
AdWordsAdvisor Says: [
Link to quote]
Good call QuAcKeR
Probably the simplest way to 'start' and 'stop' is to 'Pause' and 'Resume'. You can Pause and Resume entire campaigns, or individual Ad Groups - whichever best suits you.
One note about pausing: because statistics can be delivered to your account up to three hours after they occur, you will see clicks and impressions continue to accrue after you have paused. Never fear, these are click and impressions that occurred before you paused. However, they appear afterwards because of the server delays.