The what:
A mode that shows the borders of your monitor profile, and allows you to drag and adjust them in a few simple clicks.

The why:
I have an ultrawide monitor where I normally split the screen intro three tiles of (30%-40%-30%), having my main work in the middle, and documentations, Spotify, Slack etc. on the two sides. However, due to badly scaled webpage or app layouts, I am often confronted with having to extend the width of the windows beyond the virtual side monitor to be able to see the information on the webpage. For now, I have several backup-profiles ((33%-33%-33%), (60%,40%) etc...) that I can switch between to temporarily get a better devision, but they are often too general, and will either be too narrow or too wide. I wish there was a feature that would allow me to show the boarders of the virtual monitors and let me drag them exactly to the width I needed. Sort of how the native Windows "split screen" functionality works. Also, when re-applying the same profile again, if would be nice if the virtual monitors easily were reset to whatever was my defaul, initial setting (in my case (30%-40%-30%)).