I imagine it's okay as long as the pot isn't continually sitting in water. That is, the water flows through the pot and collects in the saucer but in the next hour or so the water in the saucer is absorbed back up into the pot and disappears.

Some plants, particularly rootbound ones, seem to have the water run right through the pot.

If however, water goes into the saucer and sits for days and days, I don't think that's good for any plant as it indicates the bottom roots in the pot will be in effect sitting in water.

What IS the purpose of using saucers with pots. I thought it was good to have a small amount of water running out the bottom. Are saucers good for anything besides cosmetic purposes?

I never grow pots on saucers unless they are indoor plants and the water would damage the floors, or they are plants that like to "have their feet wet." I would not grow a Japanese maple in a container with a saucer unless you don't water it very often. I have lost plants to root rot when their pots were on saucers, which keeps the water from fully draining. However, I do have a few plants that naturally grow in wet areas -- such as Bowles Golden Sedge -- that I grow in containers on saucers.