This whole concept can be summed up as "making the expected call".
I'll give you an example from my minor league days:
I had a "whacker" at first base on an infield ground ball with two outs and multiple base runners (I was in "C").
The play was very, very close, and I was using very, very good timing
(that is taking a long time) to make up my mind. Finally, I decided the runner was "safe". Before, saying "safe" or giving my mechanic, I noticed F3 throwing the ball back to the pitcher's mound (not to F1), the fielders trotting off the field, and the B/R taking off his helmet and batting gloves and with the first base coach waiting to take them back to the dugout.
Now what would you the base umpire do in this situation?
I think some posters in this thread would say: "You had a good long look at the play...you determined by examining all the evidence (watching the base, listening for the ball to hit the glove) that he was "safe", so call him "safe"."
Others, would do what I did: "He's out."