If you post a rear gaurd the character will be waisted as the DM would never attack your party from behind.
If you do not post a rear gaurd, you can count on the party being attacked from behind.
If the party is ambushed, enemy will spontaneously appear on all 4 sides at the same time.
If you ambush an enemy, you will learn very quickly just how difficult it is to coordinate attacks from even 2 sides.
If you shoot first, the NPC you kill will be the one whose help you really needed.
If you talk first, the NPC will prove mihself to be an enemy you can't aford to givethe first attack.
Whatever skill set you did not bring into the dungeon will prove to be the one most needed.