Hi, Tammy -
Yes, that's true, too. When plants are in containers, the minerals from your water and any fertilizer you use tend to build up. Giving those plants a really thorough watering in the tub every so often is great for them as long as you let them drain really well before putting them back in their saucers. In the winter, some tropical plants do well to have a tray of pebbles below them, with just a little water in the tray. The water provides added humidity to the plants, and the pebbles keep the plants from sitting right in the water. A cookie sheet works, as will any shallow dish.