Ad campaign delivery allows you to limit the volume of Impressions a particular advertiser/demand partner will receive along with the overall volume of incoming Ad Requests and Ad Opportunities coming from the publishers' inventory mapped to those campaigns.
QPS (query per second) parameter allows you to control the number of requests sent to the campaign in a second from the bidders added along to the waterfall. Currently, the minimum value for QPS per campaign is 100, the maximum amount is limited by your Personal Manager. The inbound amount of QPS can be spread between your RTB campaigns.
The volume of Ad Requests, Ad Opportunities and Impressions can be limited by specific time periods: daily (per 24 hours) and hourly.