The output's x,y resolution is coarser than the inputs. This is to say the feature's vertices in the output feature class are snapping to an integer grid that is more widely spaced than in the input feature class. This snapping to a coarser grid could cause feature vertices to shift slightly.
This will most often occur when moving data from a high-precision (9.2 and later) geodatabase to a low precision (pre-9.2) version geodatabase. To avoid this, use high-precision version geodatabases. If this warning does occur, run the Check Geometry tool on the result to validate that the snapping did not create problems with the feature's geometry. You may also run the Integrate command, which will snap feature vertices—between features within a feature class and in different feature classes—that are close (based on an x,y tolerance) together but due to the shift became noncoincident.