Cups With Their Trays and Saucers by Mariana Miller

Cups are often seen as a solitary vessel for the purpose of drinking. In certain cultures cups are often seen with a saucer, and the cup and saucer ( a small plate on which the cup is placed) set can be placed on a tray. Whether the process of making the set starts with the tray, cup, or saucer, each piece complements the other two.

Tom Rohr uses stoneware and/or porcelain for his pieces and even though the set below includes bowls instead of cups, the use of a tray is demonstrated in unison with the other pieces.
The function of a tray is provide a stable surface for carrying multiple dinner/drink sets. Rohr's tray would be a latter choice because of the carrying/hanging ring built into the tray's handle; forcing the carrier to make a choice between holding the tray by the bottom or carrying it by the ring. And for a final touch, the has little area for the saucers to rest on and the effect of that is the saucers would not move enough to make the entire set look unstable. Rohr has another tray set that shows how a tray can be used for a different type of cup set; in this case the set contains a sake jar and sake cups.
Focusing in just tea cups and their saucers, there is no set that exists where the design of the cup and saucer do not match. To clarify, the style of the forms and the art/coloring on the surfaces go together. Meredith Host's floral design stays constant throughout the surface of the cup as well as the saucer. It definitely makes the job of matching sets a lot easier. But the other rule for cups and saucers is that the cup must always fit perfectly into the saucer's center dip.

Sources: "Condiment Set." Tom Rohr. http://accessceramics.org/results/artist/150/

"SPIN-A Drinking Game 1." Tom Rohr. http://accessceramics.org/results/artist/150/

"Cup and Saucer Stack Set." Meredith Host. http://accessceramics.org/results/artist/260/

"Espresso Cup Set." Meredith Host. http://accessceramics.org/results/artist/260/