Most of my teaware is quite piecemeal, in the sense that I have hardly any pieces that match, besides the fact that any grouping of plain white porcelain seems to be a set. Just about all my teaware is a stand alone piece. I basically have no sets besides the one pictured.
Its an interesting question, should someone seek harmony in the appearance of the pieces, in that they are all basically identical. By that I mean same glaze, same shape same everything. I almost find this sort of cohesion almost boring, while somewhat pleasing. I have taken to creating themes with my teaware either based on glaze, shape, or artist.
For example I have a favorite pairing which is all by Deishi Shibuya, pictured below. Two of the pieces are the same glazes, while the third is a different glaze. Its actually a perfect grouping in the sense that its not identical but has a wonderful set of symmetry that it looks like they belong together.
I almost feel these set groupings are best, in the sense that few artists create pieces as part of a set. So these piecemeal groupings might actually be best.