It first appeared to me when I was fighting a WRE general with my celt warlord, both numbering 13 total with the WRE having more inherent defense/attack under VH.
So we both charged each other and I started losing warlords but I wondered what would happen if I'd use ALT and attack as I knew for archers for example it would cause them to melee...well it worked although my warlords were still using their swords (they don't have lances), they were easily killing off the bodyguard now and I ended up winning the battle.
I used this newfound trick when attacking infatry as well and noticed that I would lose more troops in the initial charge but if I switched to ALT attack while engaged, I'd lose at most 1-2 troops and then kill the enemy at almost double the speed.
I tried it for following units in BI and it works like a charm:
Any general's unit
Cavalry
Gallowglasses
Not sure if it would also work in RTW, but I would imagine so...give it a try.
Also, I think this should work with any unit that does *not* have any ranged weapon but only melee.
[This message has been edited by FactionHeir (edited 08-17-2006 @ 10:47 PM).]