Positional tolerances, in order to determine the location of features, theoretical exact dimensions and a control feature frame can determine the locations of any feature (points, axes, planes and median surfaces). The tolerance zone is located symmetrically about the theoretical centre.

For fixing locations, always use positional tolerance.
For viewing or access holes, linear dimensions may be preferred.

On the left, a cylinder tolerance zone is formed around the hole centre. On the right, a median surface is created about the two opposite surface dimensioned. In the case shown right it would create a square tolerance zone of 0.2mm x 0.2mm

Why the Diameter Symbol is Critical

If we take the extreme case and our hole was out by 0.1mm in both ‘X’ and ‘Y’ directions, the diagonal offset would be 0.14mm compared to a maximum 0.1mm in a cylindrical tolerance zone