Ads that appear in favorable ad positions on the first search results page receive more impressions than those that appear on subsequent results pages. Also, ads that appear in favorable positions on content-based webpages are more likely to be viewed by a potential customer. So, it makes sense to get your ads into those favorable positions. For more info on ad position, see What is "ad position"?
Using bid adjustments can make your final monthly spend greater than the maximum estimated spend. However, if a customer who does not match the target criteria clicks your ad, you do not pay any incremental bids.
The owner of each content-network app determines both where and how many content ads are displayed in the app. (Content ads are available only in the United States -- for more information about content ads, see How content ads work.)