TLDR: you control some units -> those units automagically become a squad. With the widget hotkey you can select a whole squad closest to your mouse cursor.
My friend (playername yyyy) made this QoL widget for unit selection that I think needs to be in the base game.
The main goal of the widget is to allow you to "select units as fast as possible, moving towards the larger lofty goal of controlling units at the speed of thought". Currently this is done by creating a new type of temporary group, called a squad. The widget automagically creates these subgroups/squads whenever you issue a command to selected units (specifically on right-click).
Then using a hotkey registered by the widget, we can quickly select any of those squads again based on proximity to the mouse cursor.
It's difficult to demonstrate how useful this is with just a video but still here's a quick demo. Please do try out the widget yourself in a skirmish game to really understand how useful it is.
For example, if you have 10 grunts selected and you move them closer to the enemy, that selection becomes a squad. You can now reselect all 10 using the widget's hotkey, without having to draw a selection box. Often this means that you only need to move your mouse to a single location (the destination).
If you in any way select 4 of those grunts and issue them a move or any other command, those 4 grunts become a new squad, so at this point you will have two squads, one with 6 grunts and one with 4 grunts. With the hotkey you can quickly select either of those squads again based on which squad is closer to your mouse cursor.
If you later reselect all 10 grunts and do a right click, the widget merges the two squads back into one.
These squads are internal to the widget, you can still have those grunts in an ordinary control group or autogroup as well.