Which delivery type shows your ads at an even pace throughout the day?
Standard delivery is recommended for new advertisers. This delivery method is useful if you want to reach customers evenly throughout the day. If you have a small budget, this method can also help you avoid spending your entire budget in the morning. Since your ad delivery occurs throughout the day, you might not see your ad appear every time you look for it, particularly if your campaign is limited by budget.
Read more here: https://support.google.com/adwords/answer/2404248