Originally Posted by
bikeforumKEN
under the comments is says ¨I used a Shimano BB-UN55 bottom bracket (118x68mm) and a 50/34T compact crankset, and had no need for spacers.¨
Different cranksets can stop at different depths on the same BB axle, so for one brand/age of a crankset you may get away without spacers and for other you might not. The overreaching rule is to have some spacers at hand and cope with the situation as it develops.