When you edit a campaign, you have to set a daily budget. If you set your budget lower than Google’s recommended budget your ads will only show occasionally. It is probably better to have a set of keyphrases that show ads continuously than occasionally. The common sense reason behind this is people often shop around. If someone clicks on your ad, looks around, goes to another site, and then tries to find your site again using the same keyphrases, your listing may not come up. If using a budget greater than the recommended budget does not work for your site, you could try using a budget lower than the recommended budget because there are various (less probable) scenarios where this might be better. Unless there are fluctuations in the times when an ad is profitable during the day, you should always make sure your ads are showing all day. If ads give positive returns, the longer they show, the more money they will make you. Some companies balk at this logic because it might mean spending thousands of dollars a month in search engine advertising. Even if there are time fluctuations in the profitability of an ad, using a budget lower than the recommended budget won’t help because Google controls when the ads show. It would be extremely lucky if your ads ended up showing only when they were generating positive returns.