Horizontal guides that alter in relation to margins
Horizontal guides that alter in relation to margins if you have to change the page sizing in document setup.
At the moment, if you need to change the page size of a document, you have to manually reset all the horizontal/row guides (e.g. Remove Existing Ruler Guides and reset the number of rows and the gutter). If InDesign automatically recalculated the guides it would save a lot of time.