Thanks for the great replies ! I'll give a few rejoinders :
check-swing appeals : The BU is asked when in the A, B or C , for both lefties and righties . It's better to be in the B/C for a lefty .
Bang-bang plays : when we are on the dirt , the runner and F3 merge into one mass of legs . On the grass the runner is approaching from the right and there is better separation of the two players and we dont view the runner's foot through the first baseman's legs .
Fair/foul : the PU has all calls down the left field line and the right field line with runners on . Rather than 85% of the time , or 67% or 75% , just make it 100% . The PU also has a better , smaller angle for fair/foul on a dropped running catch attempt .
Pulled foot : the PU always has the best angle for a pulled foot and they are definitely watching with no one on .
Swipe tags : F3's body is almost always in the way of a swipe tag . not so when BU is on the grass . I've never seen a swipe tag beyond the bag , always on the plate side , where B is .
Fair/foul over the bag : PU has the calls at 3rd already .
Umpire interference is always a risk , and happens , what , once a season or so ? With no runners on , F4 is less likely to be shading toward 2nd.
On every outfield hit , BU uses the play's first 5 seconds running inside with our back to the runner and often to the ball .
All in all , we spend two-thirds or three-quarters of the game on the grass . Lets make it 100% .