I rendered a test for a scene with full water as a second planet.
I made a render with "Displacement tolerance" of the water planet with "1" that took 51 minutes.
The render with "Displacement tolerance" at "0.1" took 39 minutes and there was no visible difference (in this scene at least).
A different test about the "Pixel reconscruction filter" differences (not related to the above) gave not much different looks.
Just the "Cubic B-Spline sharp" looked a little sharper but not much.
Not sure why there are not much difference (i expected more) but probably of the 2D motion blur i used ?