Slow then down is one of the goals. Stop if possible but no wall is ever 100% effective.
Slowing them down is good, delaying them as long as possible so sensors are tripped and an alert to Border Patrol Agents is sent and tells the Agents where the attempted breech is happening.
The border is long and remote, mostly, and an alarm tripped allows the Border Patrol Agents a location to head to so they can catch the illegals aliens at the wall or cuts down the time between the breech and arrival of the Agents.
It is what happens next that matters and really it is the only thing that matters.