It is my minor rule. iPhone applications to arrange in one page of home screen are less than or equal to 15.
The home screen of iPhone can arrange 16 applications per the page, but then a screen looks tight to me. Because the blanks of the screen increase just to reduce one application to display, I think that the appearance is better. This is my personal preference.
The number of application that you can install decreases because of this, but please try it if there is still vacant pages. You may feel slightly fresh.