In a statement designed to combat the naysayers of Ubisoft in regards to the graphical differences between Watch Dogs E3 2012 and Watch Dogs 2014, Ubisoft have said the mods/unlocking of game engine assets may negatively impact the gameplay of Watch Dogs:
"The dev team is completely dedicated to getting the most out of each platform, so the notion that we would actively downgrade quality is contrary to everything we’ve set out to achieve. We test and optimize our games for each platform on which they’re released, striving for the best possible quality. The PC version does indeed contain some old, unused render settings that were deactivated for a variety of reasons, including possible impacts on visual fidelity, stability, performance and overall gameplay quality."
The statement seems to contradict most gamers' experiences, however, with the only widely reported gameplay problem being caused by the depth of field option (which can be disabled using the same mod).