Yes, if you are good with distributed power, it can help you control run in and run out. No the slack is still there and you have to try to avoid actions which cause run in and run out of that slack. Too much slack action is both inefficient and dangerous, damaging equipment, cargo, and potentially even causing derailments.

In the "olden days" we tried to run "bunched" or "stretched". Bunched would be when you carefully gather the slack slowly, and then say begin dynamic braking. Stretched is when you have the air set and you are "dragging" train.

Don't knock slack action, though. A properly applied independent brake application, on the head end, could adjust even the attitude of a conductor like DD Burke's..... who, occasionally was known to have had a bad habit of "playing" with the conductor's valve in the caboose.

Today, without a conductor in the caboose to abuse, and the desire to "optimize" fuel use, it is my understanding, from my former peers still serving their sentences at the BNSF and UP, that running stretched is now considered "bad" train handling. And worse, the "black box" will rat you off for it, as big brother is watching.

Distributed power really helps with drag, through efficient distribution of horsepower, by placing the horsepower where it is pushing and pulling the most respective tonnage, and it is especially helpful in that by overcoming the drag from things like curvature on grades.