It all depends on what you're shooting and what your personal preference is for that shot.
Most landscape shots won't have many things drastically out of focus at sensible apertures (unless something is very close in the foreground), so without a tilt shift you can argue in some cases it's worth sacrificing ultimate depth of field to avoid diffraction softness, although equally you could argue it the other way around.
However, with a much narrower depth of field such as macro, if the depth of field is too narrow, it'll be painfully obvious even in a thumbnail sized image. Stop that lens down loads, and it'll look much better overall to everyone except pixel peepers.
In summary, do what suits you. But if you want to be as close to perfection as is possible, start saving for a TS-E lens.