archers get accuracy penalty for 3 ranks+ so I usually keep em in 2.

pikers get more supporting ranks than spear and need about 6 ranks to be fully effective IIRC.

longer front also allows the unit to wrap around the enemy's flanks.

ie. the enemy spears in 4 rans mean 25 men front while your MAA in 2 ranks have 30 men, which means the extra few guys can wrap around and disrupt the spear formation, making them break faster.

I almost always use swords in 2 and cav in 1 rank.

put them in wedge, maneuver, then slam into a flank and hit close to unfurl the gorgeous length which almost invaribaly fully envelops the suckers.