IMHO, the game as a system simply does not work nearly as well without some sort of "hard" boundry. If that is 3" fine. If others lack table space and prefer to simpy use "contact", I think that can work but only almost as well as IMO the movement rates-rules; the weapon-spell distances and the unit spacing restrictions are all related (esp. for things like charge/wild charge) and are all key elements.
I am the 3" police in our group...or was. After about 3 games each, they have all come to realize, some sort of boundry is needed and table space is never an issue with us (nor visual scale as use 28s).
If we had a small table, or something, make it 2", 1"....unit contact. But at 3", it makes the units look like "Units".
Example of a 72pt game we played a week or two back of Dragon Rampant is below. Even with my old eyes, and an (almost) entire table shot, you can see where one unit ends and the others begin and we had zero issues with withdraws, etc. It just works IMHO.
My 2 cents,