Not really enough information to answer specifically, and I definitely am not familiar with the E-190 or the QRH procedure, but here are some of my general thoughts.
First, did the QRH procedure actually isolate the fuel leak? If not, then reinstating the cross feed may (literally) piss away additional fuel. This might actually be okay if you have more than enough fuel to get to your point of landing, but may leave you short otherwise (for instance, Air Transit Flight 236, August 2001). Second, if you are actively leaking fuel as you land, it may create an additional hazard particularly if the leak is in close proximity to a running engine. Even if you shut the engine down right after touchdown, it will still be hot and could potentially ignite any fuel vapors in the area. Finally, there is the issue of lateral imbalance. Depending on the exact scenario, cross feeding may hurt or help maintain the imbalance within limits.