Without drainage many plants will die if their roots are left in standing water or wet soil. It isn’t a matter of adding the right amount of water to the pot, some of the water will end up in the bottom of the pot.
This problem is referred to as “wet feet” in gardening. It happens not only in pots but in poorly draining garden soil. Some plants like wet feet but most like a cycle of moisture, then drying, then more moisture. It is a common problem for avid new gardeners to over water thinking that it makes for a healthier plant and speeds growth, it doesn’t. It kills them.
The general rule is to poke a finger into the pot’s soil. Go about a inch and half deep. If the soil feels totally dry then the plant needs water.
It does vary from plant to plant. Some like tomatoes will wilt when they are too dry. They perk right back up when watered.
Too much water is harder to notice. Plants have a nasty habit of dying before you realize they got over watered. I’ve learned the hard way its better to under water just a little than over water.