Put Your Space Before or After?

Actually Word hasn't used cumulative spacing by default since WD2000, which is when the HTML conventions were adopted.

If you check the full thread below you will see that is confirmed by both Suzanne Barnhill and Pam Caswell.
https://answers.microsoft.com/en-us/office/forum/office_2013_release-word/spacing-before-and-after-doesnt-seem-to-be/8193c9a4-abe3-4bc4-90c0-451c07325120?page=1

@Jeanie Woodruff, when editing Normal just remember that you also need to edit the document defaults via the Set Defaults tab of the Manage Styles dialog (found at the bottom of the Styles pane next to the Options button). For the document to behave correctly Normal must match the defaults.

"Don't Add Space between paragraphs of the Same Style" is usually only set for the list styles, i.e. List - List 5, List Bullet - List Bullet 5, List Number - List Number 5.

"Don't use HTML paragraph auto spacing" is a compatibility option and can be set using a macro
Sub TurnOffHTMLParaSpacing()
ActiveDocument.Compatibility(wdDontUseHTMLParagraphAutoSpacing) = False
End Sub

@Jeanie Woodruff, I think you just need to modify the Normal style in your Normal template (Normal.dotm) with this checkbox cleared.

I, too, agree with Timothy Rylatt.

What I would like to know is how to turn that checkbox off as a default. I notice it cropping up as checked quite often, when I really never want it to be.

In my experience, all recent versions of Word have behaved as @Timothy Rylatt describes, *not* as stated in the article. However, I had a feeling that the spacing used to be cumulative, so I searched and found this thread from 2013:
https://answers.microsoft.com/en-us/office/forum/office_2013_release-word/spacing-before-and-after-doesnt-seem-to-be/8193c9a4-abe3-4bc4-90c0-451c07325120?page=1

In that thread, MVP Suzanne S. Barnhill confirms that the spacing is non-cumulative by default, but the contribution from PamCaswell still holds true: "If you want to change that, go to Word Options, Advanced, Layout Options and put a check before Don't use HTML paragraph auto spacing". I just tried that (using Microsoft 365, Word version 2002 build 12527.20988) and checking this option *does* make the spacings cumulative.

"Note the checkbox about two-thirds of the way down the dialog box entitled, "Don't Add Space between paragraphs of the Same Style." This setting controls whether spacing is cumulative between any two given paragraphs if the two paragraphs use the same style. You can set the option as desired for any of your styles."

This isn't correct either. "Don't Add Space between paragraphs of the Same Style" ignores the spacing entirely if the following paragraph is the same style. For a block paragraphs of the same style with this setting turned on the Space Before setting will only apply to the first paragraph and Space After setting will only apply to the last paragraph. All other paragraphs in the block have no space added between them.

"Remember, however, that the spacing is cumulative. For example, if you have a paragraph that is formatted for 12 points of space after it, followed by a paragraph formatted for 15 points of space before it, then there will be 27 points of space between the paragraphs."

I'm sorry but this simply isn't true. In that situation you would have a 15 point space between the paragraphs. Word simply applies the larger of the two settings.