You can apply modifiers to VI's composable objects. For example, you can prepend a 3 to the deletion operation, and delete three words, lines, or paragraphs.

You could replicate this by starting a selection and manually moving to the end (either by a combination of commands), but it looses its coherency as a single expression to be executed.

In the words of someone smarter than me, you have a conversation with vim - "delete three words", whereas you micromanage another editor - "start selection, move one word, move one word, move one word, delete".