Alternative 'Object width/height' and gap options under Effect > Transform > Move
A couple of checkboxes in that panel for the dynamic size of the object could be handy. A gap value would also be great for the static gaps around multiplied objects. I've experienced 2 similar cases where that option could save me time:
1) Create an object and use 'Effect > Transform' panel to create copies, giving a horizontal or vertical move value. Then edit the object and change its bounding box. They either overlap or the gap between them widens.
2) Create the left half of a graphic you want dynamically be mirrored onto the right side. To use the same panel first you need to copy the width of the graphic. Then in the panel, you input 1 as the copy amount, select 'Reflect X' option below and finally paste the copied width into the 'Move > Horizontal' area. So far so good. Now alter the graphic in a way the width of its bounding box changes. The duplicated mirror graphic will no longer stick to the left, editable part of the graphic. Again, they will either overlap or there'll be a gap between the two. Each time the bounding box changes you have to copy the width and edit transform values accordingly. Unnecessary time and effort.
My suggestion: If there was a checkbox next to both move directions indicating 'object width/height' as alternatives, it would be much easier and time saving to accomplish such actions. Alternatively, for those who want to duplicate a graphic n times, a user input with the gap amount could make it easier to retain the gap between copies. I've edited the screenshot of the panel with my suggestion applied.