On their own, the resolution of the wheel encoders is pretty good. With a wheel diameter of 72 mm, and 508.8 counts per revolution, there is about 0.44 mm per count. And the angular resolution is also good. Turning in place with 1 encoder count yields 0.00378 radians (0.217 degrees).
Unfortunately, for motions like going forward 10 m, the robot can only perform open-loop control. Because there is no overarching ground-truth to close the loop. (For example with a motion capture system like OptiTrack). So the robot is at the mercy of environmental factors like carpet drift, differences in wheel diameter, differences in motor torque, wheel slippage, etc. This, combined with low-cost electronics which limit the resolution of the velocity controller (about 28.5 mm/s per step), make it so the robot might not actually drive very straight.
As I mentioned earlier, this is largely due to external conditions so iRobot makes no claims regarding the accuracy of the Create2. It is up to you to test under your own conditions.
P.S. All specs above are mentioned in the OI Spec document.