Google has recently released a new feature called Shared Budgets in AdWords. It allows advertisers to utilize one daily budget to be utilized across multiple campaigns in an AdWords account. This new feature will allow advertisers to manage AdWord’s daily budgets in each campaign more effectively and efficiently.
A useful way in which this feature would be utilized is when you have multiple campaigns targeted to different devices (desktop, mobile and tablet). Previously, advertisers would have to decide how to allocate budget for each campaign and set those budgets in AdWords for each campaign. However, on any given day one campaign might not spend out their entire budget and the other two do. Unless the advertiser shifted that unspent budget in AdWords, that unspent budget is now lost impressions in the other campaigns. The advertiser would have to manually go into AdWords and shift the budgets between campaigns to hit the daily budget. But now with the shared budget feature, budget automatically adjusts budget to each campaign. This eliminated the need to for you to constantly monitor budgets across your campaigns.
To implement this feature, log into AdWords then go to Shared Library and click on budgets in order to create a new shared budget.
Source: Google Inside AdWords Blog