"rem" units can be scaled up or down globally by changing the font size on the root element. This can help in creating a consistent and scalable design without having to manually adjust every element size.

While "rem" has several advantages, it's important to note that there are scenarios where "px" may still be appropriate, such as when you need to create fixed-size elements that should not change based on font settings. Additionally, it's common to use a combination of both "rem" and "px" units in a CSS stylesheet to take advantage of the benefits of each in different parts of the design.