Ole Anderson lambasts the written guaranteed contract in his autobiography, contrasting this with talent being paid a percentage of the gate. He presents considerable evidence from the late 1980s and early 1990s showing World Championship Wrestling (WCW) spending lavishly for talent, ostensibly with little regard to how such contracts will effect profits and attributes this change in wrestling economics to the "Suits" (corporate interests with no background in wrestling).
I found this coverage fascinating, especially Ole's coverage of the ballooning of talent contracts down the roster. While spending lavishly for top stars, especially when trying to compete with the WWF makes some sense for WCW, similar spending for mid-card and lower talent does not. Ole suggests this shift to written guaranteed contracts breeds laziness as a talent's earnings are not connected to the company's nightly earnings or the quality of shows. I'm not sure how wrestling promotions could feasibly work nationally without written contracts, but these contracts, especially in a company headed by those with limited to no experience in wrestling, change the dynamic of booker-talent relations that appears to limit coherent story designs. One should also take particular notice to how Ole suggests that Vince McMahon has been able to overcome these constraints.
With the current lack of meaningful competition for the WWE, I'm unsure whether the guaranteed salary contracts are still necessary. Certainly the WWE has clear rationales in preventing talent from working elsewhere (see Alberto del Rio as of late), but the performance-based pay would seem to encourage innovation. A change might even make Ole's day.