Advancing units must move the full distance rolled, in the same direction towards and through the enemy if they outpace them. If this brings them into contact with fresh enemy they move directly into base contact, effectively assaulting the enemy and beginning another close combat.
No further combat is fought during the turn that the advance is made; combat is, instead, fought in the following turn. The advancing unit is considered to have launched an assault that turn, and receives the normal +1 Attack bonus.
Diagram: The Space Marine squad sweeps into a second Dark Eldar squad that is only 8" away.
Errata — Chapter Approved: Main Rules Clarifications (v2.0): Models that are charged in a sweeping advance may fire their weapons as if they had been stationary during the Movement phase.