As you can see, I'm a fan of grids (Ha! It's the way I tell 'em). If nothing else, a subject with true verticals and horizontals is a good test of your camera technique. It's also a good test of your fusspot quotient: do sloping horizons or converging verticals bother you? More to the point, does it even occur to you to notice them?
I confess they do bother me more than I'd like to think, but only in this kind of shot, where getting them "wrong" would be so noticeable (or a conspicuous and provocative act of anti-fusspot-ness). Lee Friedlander can slope those pavements all he likes, as far as I'm concerned -- it works. Although I'm a 100% hand-held photographer, I do tend to notice and straighten verticals when composing in the viewfinder, although I do have a tendency always to raise the horizontal to the left.
In fact, if I had to name one simple thing that had improved my work, it would be "paying attention to vertical edges" and, for most purposes, trying to keep them parallel to the edge of the frame (i.e. not pointing the camera up or down). If nothing else, it means you often have to try different angles of approach, or using the "built in leg zoom", which often means finding better pictures.