Example
Half closed at +1R and half at +3R averages +2R.
In practice
Taking some profit at a first target locks in a gain and makes the rest of the trade easier to hold. Many traders combine it with moving the stop to breakeven on the remainder.
It is a compromise between two exits: a fixed target that guarantees a result, and a runner that can catch the occasional large move.
What to watch for
Scaling out lowers the average win, since only part of the position reaches the far target. Over many trades it can earn less than holding the full position, so test both ways.