I need help with why I should not use numbering in headings, for example:

Chapter 3
Section 3.1 Screens Shots
Section 3.2.1 Graphics

For instance someone is questioning to a particular section over the phone or via email they can just refer to the section number.

I have been told by an editor that he/she does like numbering style as it could make the header look to busy.

When did the use of this numbering style start?
What type of industry is it best adapted too?
Should it be used?

In the book I'm doing the chapter is numbered and figures, tables etc are numbered accordingly. So I have Figure x.1, x.2 etc then Table x.1, x.2 etc.

Using outline numbering (3.2.1) is overkill, but using a chapter then sequential number is standard for technical books.