Not a question, just a tip. When doing a grid fill on a square or rectangular area, make one of the corners the active element. That will fill perfectly without touching the span or offset controls. (assuming the existing geometry has equal numbers of edges on opposing sides.)
Great tip ddatacable !
Its quite common in Blender, and not well known, that the active element is the base point for most tools.
Another example is the checker deselect, under the select menu.
A great time saving tool I use quite often. Even if it requires reselecting one or two verts for exactly what I need.
