If this is Rotate Section of Harness action we're talking about then the increments of the angle are determined by style set settings under Style Set > Design node > General Settings >Design Settings; there's a setting on the RH side called RoationAngleRoundingValue. This is what you are looking for.
When using this piece of functionality, pressing CTRL key will give you the absolute angle that the section (bundle) is making with the horizontal, rather than the default, which is the difference in angles before and after. Polar and Grid settings have nothing to do with this.
Note that using this functionality, the angle is shown as transient graphics (in red) as you rotate.
Otherwise, if you meant rotation as in "stretching" the bundle by dragging its end, then Polar settings come into play "rotation-wise" as follows:
Polar off: no constraints on bundle angle
Polar On: angles allowed are: angles of bundles that meet with the selected one at the rotation point (junction), or increments of the setting in style set that was previously mentioned.
To turn Polar mode on/off: SHIFT+P
Hope this helps