Actually 0.8 isn’t even the limit! There’s the term “nozzle flat size” which is the total diameter (bore + wall) of the bottom of the nozzle. Bambu nozzles appears to be 2x the bore, so a 0.4 nozzle has a nozzle flat size of 0.8 mm. Also, the cross section of the extruded line isn’t a rectangle but has a semicircle on each side (i.e. a stadium), and this adds to the maximum line width with half of the layer height at each side.
So the proper formula for maximum line width is nozzle_flat_size + layer_height, which in our case is 2 * nozzle_size + layer_height and for a standard layer height of half the nozzle size, it’s as simple as 2.5 * nozzle_size.
With a 0.4 nozzle you can thus print 1 mm wide lines at a layer height of 0.20 with good quality. Bambu Studio had an off-by-one bug that I recently fixed, so you had to say 0.99 mm. Latest beta does accept 1 mm.
I’ve used such widths in testing and it comes out really nice - but due to volumetric flow limitations you may trade speed in mm/s for speed in mm³/s (total print time should not change much though). An example of use case for this is overhang - with 1 mm line width you can do twice as steep overhangs as with the standard width! Another obvious example is vase mode (a.k.a. spiral mode).
Edit: typo