If you have two windows and you resize the other and the borders touch they should snap just like if you had moved the first window next to the second. Reproducible: Always Steps to Reproduce:
That would be cool indeed! Olivier?
Dunno. Resize code is already very complex bcause of partial struts and all kinds of checks, I'm not sure I really want to add more complexity to that code.
This is a feature that I've gotten very used to with Openbox. Managing windows (tiling out a workspace) is made vastly easier with this ability.