BBB terrain maps at 2/3 size but I didn't fully explain how I came to that idea in the first place.
BBB scenario maps are very considerately designed for a standard 6' x 4' wargaming table. I can create an area of that size at home but it requires extension boards. It would be a little easier to play on my dining-room table without extension boards. Also, my 10mm American Civil War armies use 20 mm bases (rather than 1" bases) so the 2/3 size is a better proportional fit. (To be exact the bases are 40 mm wide, but I am counting them as double bases and making up some 20 mm wide ones for singles.)
Another advantage of the reduced size is the ability to print the 8" map squares 2-up on A3 paper. This means I can play on the printout of a map rather than having to set up 3D scenery. There are times when this could be advantageous.
It's obviously a good option for my ACW armies but I was also considering it for any future armies so I floated the idea on the BBB Yahoo Group. Rules author, Chris Pringle, suggested combining the 2/3 map size with normal size bases but reducing the number of bases in each unit. I didn't immediately warm to this idea but then I realised it would allow me to play at both scales without irretrievably committing myself to smaller bases.
For someone of my clumsiness 1" bases are fiddly enough! In extremis I could also borrow the 1" square bases from my Seven Years War Maurice armies.