BB spindle length
I'm getting ready to buy a replacement for a worn out shimano lp26 68x116 bottom bracket. It looks like 116 isn't an option for spindle length on the newer shimano bb's (i'm planning on getting a un54), but they have 115 and 118. Sheldon's bb size database lists the usable lengths for my crank at 116-121, so I'm going to order the 118 length.
I know it's only 1 or 2 mm difference, so I guess this question is mainly for curiosity, but what (if any) effects would changing the spindle length have? Does it just mean having to adjust the front derailleur? Does a shorter spindle length give you a 'better' chainline?