Short Answer
Yes.
Explanation
It is a good practice since an element can be a part of different groups, and you may want specific elements to be a part of more than one group. The element can hold an infinite number of classes in HTML5, while in HTML4 you are limited by a specific length.
The following example will show you the use of multiple classes.
The first class makes the text color red.
The second class makes the background-color blue.
See how the DOM Element with multiple classes will behave, it will wear both CSS statements at the same time.
Result: multiple CSS statements in different classes will stack up.
You can read more about CSS Specificity.
CSS
.class1 {
color:red;
}
.class2 {
background-color:blue;
}
HTML
Live demo
It’s a good practice if you need them. It’s also a good practice is they make sense, so future coders can understand what you’re doing.
But generally, no it’s not a good practice to attach 10 class names to an object because most likely whatever you’re using them for, you could accomplish the same thing with far fewer classes. Probably just 1 or 2.
To qualify that statement, javascript plugins and scripts may append far more classnames to do whatever it is they’re going to do. Modernizr for example appends anywhere from 5 – 25 classes to your body tag, and there’s a very good reason for it. jQuery UI appends lots of classnames when you use one of the widgets in that library.