conflict of making your document smaller than your margins
InDesign CC 2019 v. 14
The New ”New document” dialog box doesn't give any warning of the conflict of making your document smaller than your margins allow. It just changes the width and/or height back to what it was as a default if your margins are too large and does not warn the user about it.
And if the user fails to notice that the size switches back, it will create a document that’s not the size intended. User may not even realize what is it that went wrong.
In the Legacy New Document dialog box, when you click OK, it will warn you of the conflict with an error message and you can’t move forward without correcting the conflict. This warning is really helpful. Please bring it back.
InDesign is trying to be helpful here by intelligently reverting to the last good value in the New Document dialog since it’s not possible to create a new document with the values entered by you.
We hope you find this useful.
Adobe InDesign team
Sorry to say but it is terrible UI design, it does not work at all. So a value is changed but there is no indication to the user that it was changed. The old warning box was much more visible and clear and forced the user change the values themselves. This is not something InDesign should be helpful about.