I think it's cleaner. Instead of doing:
```javascript
var x = obj.someMethodThatReturnsAClassSpecificResult();
switch (x) {
  case CLASS_1_SPECIFIC_RESULT:
    // ...
    break;
  case CLASS_2_SPECIFIC_RESULT:
    // ...
    break;
  // etc.
}
```
I think its cleaner to do:
```javascript
if (x instanceof CLASS_1) {
  // ...
} else if (x instanceof CLASS_2) {
  // ...
} // etc.
```