Reach - BidTheatre DSP reaches across several sources of ad inventory, including many ad networks and media houses
Transparency - BidTheatre DSP is transparent with what sites you are running, and their prices. The ad network usually has a degree of opaqueness to what where your ads are served and the distribution of them across sites
Freedom to choose - BidTheatre DSP lets you choose exactly what domains to bid and buy from, and what not to. Ad networks usually bundle several sites in "Run-Of-Network" solutions. Some of them attractive, some of them usually less attractive.
Maximum CPM instead of fixed CPM - prices are varying and determined in real time according to market mechanisms. You decide what you're willing to pay at a maximum.
Both branding and performance - depending on what you choose to target, the DSP can be used both to drive initial awareness or end conversions.