Why use "need not" instead of "do not need to"?

Question

The header of psyco.sourceforge.net states: > High-level languages need not be slower than low-level ones. Why use *need not* instead of *do not need*? What does it mean? Also, why no *to* before *be*?

Answer 1

There is absolutely no grammatical difference and no difference in use. It is simply personal preference.

I can tell you that people who turn it around (need not) are usually extremely well versed in the English language and like to use a lot of variety in their speech, OR are very "proper" in their speech and manner, OR come from a background where people are more formal in their speech (like the British).