There are many different knob types in a home (hand knobs for example). What kind can you expect to deal with the most out of plastic and metal? That’s what we’re here to discuss!
When looking around a typical home, you probably see metal a lot more because it’s more secure on doors. Doorknobs that are metal are easy to install and use. They also lock and can be used with any kind of door type like the entrance of your house or side garage door that leads into your home.
Plastic knobs are useful as well (are there also plastic handwheels?), but they don’t seem to appear quite as much in a home. They usually are used on windows or things like cupboards. It’s hard to make sure that these are secure, but they do make some that act as secure latches for windows.
Another use for plastic knobs is in the bathroom. Look to a lot of the typical hot and cold ones that you can use easily to change the temperature of the water. You can’t really use metal a lot of the time that’s cheap because water can rust it and make it stain the area around it while plastic is okay when wet.