Hitting twice forces opponent to hit back more compared to being able to dodge doing that sometimes with only one checker hit. Also if do get hit 2 pips of timing have been saved in the outfield.
As an example consider a 41 reply after being hit once. Hitting from the bar looks to be an error.
           
 
         
 | | White is Player 1
score: 1
pip: 108 | | 7 point match | pip: 165
score: 0
Blue is Player 2 |
|
| XGID=aaAAcBCBBB--A--A-bacb---b-:1:-1:-1:41:1:0:0:7:10 |
| Blue to play 41 |
| 1. | XG Roller++ | Bar/24 8/4 | eq: -0.6842 |
| Player:
Opponent: | 23.21% (G:1.85% B:0.03%)
76.79% (G:25.79% B:1.90%) | |
|
| 2. | XG Roller++ | Bar/24 7/3 | eq: -0.6936 (-0.0094) |
| Player:
Opponent: | 22.94% (G:1.87% B:0.03%)
77.06% (G:26.05% B:1.90%) | |
|
| 3. | XG Roller++ | Bar/24 6/2 | eq: -0.7037 (-0.0195) |
| Player:
Opponent: | 22.76% (G:1.65% B:0.02%)
77.24% (G:26.31% B:1.98%) | |
|
| 4. | XG Roller++ | Bar/21 24/23* | eq: -0.7982 (-0.1141) |
| Player:
Opponent: | 18.93% (G:4.72% B:0.16%)
81.07% (G:29.16% B:0.88%) | |
|
| 5. | 2-ply | Bar/24 5/1 | eq: -0.8621 (-0.1780) |
| Player:
Opponent: | 17.69% (G:1.17% B:0.02%)
82.31% (G:28.61% B:2.08%) | |
|
eXtreme Gammon Version: 2.10, MET: Kazaross XG2