A drainage hole lets excess water leave after the potting mix has been wetted. Without one, salts accumulate more easily and the lower layer may remain saturated even when the surface looks dry.
Watering should be thorough
Small sips can leave dry pockets and encourage roots near the surface. In a draining pot, you can wet the mix evenly, wait for excess water to escape, and empty the saucer or outer pot.
Cachepots are useful when checked
A decorative container can hold a smaller nursery pot. Remove or lift the inner pot to water, let it drain, and ensure no water remains trapped at the bottom before returning it.
Adding stones is not drainage
A layer of stones inside a pot without a hole does not create an outlet. It reduces the volume available to roots while water still collects in the container. Use a real drainage path whenever possible.