The point is to use the mouse for window management not just on the applications. Now, i haven't used i3, but from a tiling window manager i'd expect at minimum that i can drag-drop windows with the mouse between "zones" and resize the zone boundaries interactively with the mouse.

For extra stuff i'd like using the wheel up/down on a title bar to minimize/restore a zone, drag-dropping a window over another window to create a zone made out of tab-like title bars, ctrl+clicking multiple titlebars to select multiple windows (so that, e.g, drag-dropping them to another zone would put all of them as tabbed windows in there or being able to close all of them either via a shortcut or via a popup menu command, and/or commands to merge them in one tabbed zone, or split tabbed zone(s) to individual zones), right clicking on a zone separator to offer a popup with commands to split/merge the zone, move the splitter at some specific percentage, etc, drag-dropping one or more windows at the edge of the screen to create a new zone (or set of zones for multiple windows).

There are so many things you can add with a mouse, especially if instead of thinking of it as a car vs horse you think of it as what it actually is: an additional input device that is right next to your keyboard and unlike the keyboard it provides precise analog input for 2D motion.

As a starting point you can check what pretty much every IDE with support for tiling does (e.g. the recent versions of Visual Studio - not VSCore, the real one).