These are the side and top / bottom margins of your home screen, and you want the widgets to have as much vertical or horizontal space as possible. (howtogeek.com)
By removing side margins, bottom margins etc... you have to learn how to read all over again. (blog.the-ebook-reader.com)
Also, your top and bottom margins don't have to be the same size as their left and right side counterparts. (resume-library.com)